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1. password aString Set the password used to verify user logon password aString userName Answer the userName If it s nil it should default to an empty String userName isNil iffrue userName userName userName aString Set the account name of the user loggin on userName aString edge pertaining to the local host s GUI is kept isolated in a small hopefully mostly automatically generated layer Di alects of Smalltalk vary most widely in how they describe their user interface mechanisms In applications designed us ing the ICM approach the portable Control code and the nonportable GUI specific code are not all run together in a single layer This allows applications to be moved between Smalltalks very rapidly E Greg Hendley is a member of the technical staff at Knowledge Systems Corporation His OOP experience is in Smalltalk V DOS Smalltalk 80 2 5 Objectworks Smalltalk Release 4 and Smalltalk VPM Eric Smith is a member of the technical staff at Knowledge Systems Corporation His specialty is custom graphical user interfaces using Smalltalk various dialects and C They may be contacted at Knowledge Systems Corporation 114 MacKenan Drive Cary North Carolina 27511 or by phone 919 481 4000 THE SMALLTALK REPORT MALLTALK IDIOMS Kent Beck Why study Smalltalk idioms y dictionary defines an idiom as a phrase whose meaning cannot be predicted f
2. Doug describes a technique for using existing PM messages to let Smallralk V PM communicate with OS 2 threads thus providing Smalltalk pro grammers with more control over their applications behavior This month marks the debut of a series of articles on Objectworks Smalltalk by Dan Benson from the University of Washington In Release 4 ParcPlace made many fundamental changes to the architecture of the graphics and user interface classes As David Liebs and Kenny Rubin de scribed in last month s issue the changes were necessary and overdue Unfortunately the in depth explanations and good examples needed for programmers to comprehend the changes were sadly lacking Over the coming months Dan will develop a simple graphics application he calls Small Draw His first article introduces graphics concepts and application construction with the MVC ar chirecture through the definition of a minimal SmallDraw This simplified version demonstrates interactive creation of geometric shapes and display of graphics Future articles will extend the functionality of SmallDraw by adding selection translation scaling alignment using a DialogView and grouping of objects vertical and horizontal scrolling of the view a cut copy paste clipboard and support for command keys It is our pleasure to welcome another well known Smalltalk guru Kent Beck to the ranks of SMALLTALK REPORT columnists Kent has been involved in many successful Smalltalk projec
3. Easing into objects developing the object components industry David A Taylor OBJECT MAGAZINE 3 4 92 The changing nature of systems however including a move to dis tributed development and deployment the increased use of graphical user interfaces improvements in language and environment technol ogy and widespread availability of classes and libraries will speed the adoption of object oriented programming languages Large systems of the future will evolve on a project or functional basis rather than as multi year phased systems As the world migrates to reusable components and the development of organic systems small methods will once again dominate A method like IE based on the mainframe centric master enterprise model view of the world will ultimately collapse under its own weight When objectified versions appear view them with caution and ask if the problems they are solving will be relevant to you by the time you complete your enterprise model Methodology objectified information engineering the method time bomb Adrian Bowles OBJECT MAGAZINE 3 4 92 Relational vendors believe that by extending the capabilities of their database servers or the capabilities of some front end tools many of the benefits of object technology can be achieved without THE SMALLTALK REPORT adopting a new database model Sybase s VP of marketing Stewart Schuster referred to object technology as a natural extension
4. For example someone named Terry terry galaxia new port ri us writes I would like to open a discussion about multiple in heritance in Smalltalk To begin with could someone who knows the history explain why Smalltalk does not have m i Here are my suggestions for multiple inheritance Ralph Johnson johnson cs uiuc edu replies with a sum mary of the history The folks at Tektronix claimed to have fixed lots of bugs but they still kept running into problems and finally decided that it wasn t worth it Implementing m i this way can be done entirely in the image You don t need to know anything about how the v m is imple mented So anybody out there who wants to implement m i can just go ahead If you are successful and can make something that people want to use then you will be famous though probably not rich STRONG STATIC TYPING Another significant difference of opinion on programming languages is the matter of static vs dynamic typing In fact 66 Many of the people on the net are reasonable unprejudiced and willing to accept differences of opinion Unfortunately a lot of them aren t 99 the existence of this argument represents one of the most re markable achievements of C Almost overnight it turned more C programmers than would have believed possible into resolute defenders of strong typing They along with Eiffel programmers will argue that strong static typing is es sential fo
5. anObject code to add anObject self changed add Our view would be set up to look for that particular aspect add invalidating itself to be refreshed when found while ig noring all other aspects update anAspect add anAspect iffrue self invalidate Controllers come into play whenever input comes from the mouse or keyboard A controller usually takes control of input events whenever the cursor is in its view It can be set up to check for keyboard events or mouse clicks taking action when appropriate Some controllers know about menus and how to process them for their respective views A controller dealing with a menu will often direct the menu selection to it self its view or its model The MVC notification mechanism is automatically inher ited when we define our application components to be sub classes of Model View and Controller Let s begin our appli cation by describing the model where the information of interest is stored and processed In this case the model will be the SmallDraw object itself The primary information it will keep track of is the set of graphic objects that are drawn Ad ditionally it will maintain a current inside color border color and line width that each new object will be assigned These values will be initialized when the application is invoked but will be able to be modified through menu selections The SmallDraw model will need to provide methods for adding new objects to the dra
6. free software First there are no guarantees and no toll free customer support hotlines The code may be badly written poorly docu mented or nonportable You may be able to get someone possibly even the author to help you with any problems but you may not I haven t personally used any of the pack ages described above so don t take this mention as an en dorsement of any kind Second there may be restrictions on how the code may be used Many authors retain copyright on the packges Using all or part of the package in a commercial product may require an arrangement with the author or may not be allowed at all Carefully read anything concerning copyright or licensing agreements Large packages are more likely to reserve rights than goodies The authors of T Gen and the Smallmusic packages retain the copyright on the software MANCHESTER GOODIES BY FTP One of the archives I mentioned last issue is at the University of Manchester in England Recently this archive became ac cessible by ftp The machine is called mushroom cs man ac uk an alias for 130 88 13 70 and the files are available in the di rectory pub goodies This machine and the archive server at the University of Illinois should now contain exactly the same material Questions about the archive can be addressed to lib manager cs man ac uk SMALLTALK CHAT SESSION Internet Relay Chat or IRC is a real time computer confer encing program It allows people with d
7. rather than a fundamental paradigm shift Mary Loomis VP of technology for Versant Object Technology noted that RDBMSes have stored procedures and BLOBS but claimed that was not ade quate They are baby steps Loomis said Some RDBMSes have stored precedures which begin to put some actions in the databases but they re in a very limited way They really don t couple the data with the action Object databases are much more than BLOBS SPARC databases square off Barry D Bowen OPEN Systems Topay 2 17 92 According to the January February 1992 issue of PC Al the value of the relational database market in 1980 was 2 million but in 1990 it was 2 5 billion Similarly the value of the object oriented market today is 10 million By 1995 PC Al estimates the value will sky rocket to 235 million Quick statistics COMPUTOR EDGE 2 7 92 Now they re scrambling to recreate their CASE programs to write software for desktop machines and local area networks Many of the big mainframe CASE vendors including IBM Texas Instruments Inc and Andersen Consulting are already coming out with new products for these markets Otherwise there will be a reapportioning of IS dollars in favor of smaller CASE vendors Such as object oriented programming environments AT amp T for instance is using an object or ented CASE program called Teamwork from Cadre Technologies Inc of Providence RI to build a piece of its 9
8. s menu before processing By contrast most commercial applications provide a palette of drawing tool buttons for selecting the type of shape to draw So far here is the hierarchy of SmallDraw MVC applica tion classes we ve described Object Model dependents SmallDraw objects insideColor borderColor UneWidth VisualComponent VisualPart container DependentPart model View controller VoL I No 7 MAY 1992 10 E SMALLDRAW RELEASE 4 GRAPHICS AND MVC SmallDrawView scale Controller model view sensor ControllerWithMenu SmallDrawController MVC INTERACTION Because views and controllers are often designed to work closely together views often specify and even create their own controllers When the SmallDrawView needs to create its controller it will ask its defaultControllerClass for one All we need to do is provide a SmallDrawView instance method that specifies the correct controller class defaultControllerClass S mallDrawController Connecting our MVC triad together is accomplished by specifying the model when the view is created aSmallDrawView SmallDrawView model SmallDraw new From this single message the view knows its model and the model s dependents include the view When the view creates its controller the connections are completed It may be interesting to look at the message selector inter actions bet
9. service The object ori ented technology combined with CASE programming capabilities says AT amp T systems engineer Michael Krass lets the company write code that can be easily reused and maintained unlike traditional CASE The case against CASE Robert Moran INFORMATION WEEK 2 17 92 Sun Microsystem s R G G Cattell made a couple of observations on choosing among the available object databases For the object database in question look at the power of the query languages for associative retrieval or queries across sets of objects Second how well are they integrated with a programming language In some ar eas the differences among commercial offerings are minor Based on the Cattell benchmarks there is not much difference in perfor mance among the object databases Further more the size of the benchmark database is not important There is no storage require ment penalty He said he would choose a database largely on the basis of the company and its stability The technical differences are small What about writing your own would lean toward buying Cattell said You can always build something faster relative to what you can get off the shelf but the performance of the commercial ob ject databases is quite impressive Guidelines for choosing the best database technology Robert H Blissmer ELECTRONIC ENGINEERING TIMES 2 17 92 Gartner Group s David Stein Object technology is probab
10. Presentation Manager PM message processing thread and a Smalltalk code executor thread This design is based on a PM requirement that an application re turn control to it quickly after processing a message Since a PM message might and usually does cause Smalltalk code to be executed this PM requirement could not be guaranteed us ing a single OS 2 thread In the two thread implementation a PM message is pro cessed by adding it to a global OrderedCollection named Cur rentEvents by the PM message processing thread This thread immediately returns control to PM allowing other applica tions to process their PM messages Some typically very short time later the Smalltalk code executor thread checks the CurrentEvents collection to see if there are any messages If any are pending they are routed to their respective win dow objects Class NotificationManager performs this service for the code executor thread See its instance method run for more details Since PM messages are identified by a unique message number VPM must have a way to translate between message VoL 1 No 7 May 1992 numbers and method names This translation is done by us ing two global objects PMEvents and PMEventsExtra PMEvents is an array of symbols indexed by PM message number That is PMEvents at 7 contains the value wmSize with Seven is the message number assigned to the WM_SIZE message by PM The PMEvents array is not large enough to map e
11. The Project Class Browser is an enhanced Class Hierarchy Browser which supports tracking of class and method changes for a project and adds several productivity enhancements Version 1 0 supports Smalltalk V PM amp Windows and is available now for 99 95 5 shipping 20 outside the U S in Ca please add 8 25 sales tax Includes source code object libraries PM and user manual 279 S Beverly Drive Suite 217 Beverly Hills Ca 90212 Voice 213 878 2327 CIS 71031 2640 graphics context scaled by the view s display scale As an aside if we wanted to we could design our application win dow to contain two SmallDrawViews with one at normal size and the other enlarged or reduced Each would be a depen dent of the same model but would provide different perspec tives of that model We ll also need to define our own SmallDrawController It will be responsible for handling all user interaction from the mouse and keyboard The two main functions of the con troller in this application are handling menus and drawing new objects If we make it a subclass of ControllerWithMenu it will inherit the ability to handle menus When the operate button is pressed the controller usually obtains the menu from its view and processes it For simplicity s sake we ll choose the type of object to draw from a menu Since the con troller handles the drawing of new objects we ll have it add its own menu selections to its view
12. and processing and the user interface the part that handles input and output The user interface is divided fur ther into View which is responsible for visual output and Controller which is responsible for user input such as from the mouse or keyboard Separating the user interface components from the infor mation model makes it easier to plug in other interfaces to the same model connect multiple interfaces to a single model or reuse interfaces for other models The Smalltalk system is full of examples of using the same kinds of interface compo nents for different sorts of models For instance take a look at the SystemBrowser or the FileList utility A model can have any number of views whereas views are usually attached to a single model Each view has only one controller or none if it doesn t require user input and each controller has only one view While the model is indi rectly connected to its view through its dependents instance variable the view and controller have instance variables tying them directly to each other and their model as shown in Figure 1 The model communicates with its interface components through a dependency mechanism Each model maintains a list of its dependents and notifies them whenever changes are made to the model s state These dependents can be any kind of object but are usually one or more views A view keeps an eye out for certain changes in its model When it detects any of those
13. be included in any Smalltalk V developer s environment Jim Salmons The Smalltalk Report September 1991 Cooper amp Perens Inc rornmeny ACUMEN SorTwane method will return the resulting rectangle scaled to the view s coordinate system rectangleFromScreen Answer the resulting rectangle obtained from the user in the views coordinate system Assume the mouse is already pressed origin rectangle polygon screen lastPoint start newPoint screen Screen default start lastPoint self sensor cursorPoint origin self sensor globalOrigin rectangle Rectangle origin start comer lastPoint polygon Array new 5 withAIL start self sensor anyButtonPressed whileTrue screen displayShape polygon lineWidth self rubberBandLineWidth at origin forMilliseconds self rubberBandDelay newPoint self sensor cursorPoint lastPoint ifFalse rectangle Rectangle vertex start vertex lastPoint newPoint polygon at 1 put rectangle topLeft at 2 put rectangle topRight at 3 put rectangle bottomRight at 4 put rectangle bottomLeft at 5 put rectangle topLeft rectangle scaleBy self view displayScale reciprocal WINDOWBUILDER The Interface Builder for Smalltalk V 2600 E Camino Rea Sume 609 Pato Alto Cauronnia 94306 The key to a good application is its user interface and the key to good interfaces is a powerful user interface development tool For Smalltalk that too
14. changes it will update itself by displaying certain as pects of its model Whenever the model changes its state in a way that may be of significance it sends itself one of the following messages self changed self changed aSymbol self changed aSymbol with anArgument Which message is used depends on how much detail is nec essary For instance the changed message is the most general and simply informs the dependents that the model has changed in some way but it doesn t tell them which aspect of the model has changed Some views might only be interested in a particular aspect of the model so additional information can determine whether or not they will respond to the change The changed methods are found in the Model instance methods Each changed message is eventually transformed into an appropriate update message that is broadcast to the list of dependents The dependents must have a correspond ing update method in which they redisplay themselves or take some other action THE SMALLTALK REPORT update aSymbol with anArgument from aModel update aSymbol with anArgument update aSymbol update Upon receiving an update message a view will usually redis play all or a portion of its model For instance in our Small Draw application when we add a new graphic object to a draw ing the view should be notified so that it will redisplay the drawing Our model would do something like the following addObject
15. column Other versions of Smalltalk V have different implementa tions and a different version of the code is necessary to imple ment class instance variables MetaClass class subclassOf aClass Modified This is the instance creation method for MetaClass and is a private method It is modified so new instances of metaclass have the structure of their superclass In the original version of this method each metaclass was created with the structure of the Class class MetaClass methods instanceVariableNames stringOfInstVarNames New This is a new method representing the public interface for class instance variables This method is used to redefine the instance variables for a class class instance variables The ar gument to this method is a string containing names of class instance variables The argument is the same format as for in stance variables and class variables Class fileQutOn aStream Modified This method has been modified to write the definition for class instance variables The result of this method is also used to print the definition of a class in the browser The string defining class instance variable always prints even if there are Listing 2 Extended Class Definition for AnimatedObject Object subclass AnimatedObject instanceVariableNames position oldPosition jumpIncrement direction goCount classVariableNames poolDictionaries WinConstants AnimatedObject class instanceVariableNam
16. even when the non Smalltalk parts are running in their own threads INTERFACING YPM TO OTHER PRODUCES One common requirement is an interface between application programming interfaces APIs provided by third parties and the VPM enviroment Typically these APIs are packaged as one or more dynamic link libraries The most obvious way to provide the in terface is to follow the VPM developer s guide and create a subclass of DynamicLinkLibrary DLL While this works for DLL calls that return control rapidly it fails when control is kept for any length of time The effect of this failure is to hang the workstation until the DLL call rerurns To see this for yourself evaluate the following with Do it DosLibrary sleep 10000 This will cause your entire workstation to hang for the 10 seconds it takes DosSleep to return control Clearly if you can t guarantee the DLL call will return control quickly an other implementation must be found This causes particular problems for communications packages since the time it takes to return control depends on the network and the partner program In fact all of the research for this article was done while developing an APPC interface for VPM SOLVING TLE INTERFACING PROBLEM To an OS 2 C programmer the solution to this problem would be simple Create another thread of execution and let it wait for the response from the DLL call In the VPM envi ronment however life is a little more complicat
17. for this application interface interface anObject Set the object which implements the interface layer for this application interface anObject rating the Control from the Interface the more volatile as pects of the application are isolated from the more stable portions This protects the stable code from the ravages of constant change PROJECT MANAGEMENT The design of the presentation of an application and of its control though related involves different skills In some or ganizations different developers would be given responsibil ity for these areas If the application is designed with a monolithic user interface the two developers work will be hopelessly mixed and mingled By using the ICM architec ture their work would be cleanly divided Also the protocol by which their two components communicated could be easily defined PORTABILITY One of the strongest reasons for using the ICM architecture is that it leads to applications that can be ported from one di alect of Smalltalk to another very rapidly All of the knowl model Answer the domain model ie the guy who knows about accounts passwords and logon verification model model aSystemLogonManager Record the object I can ask to verify logon requests model aSystemLogonManager password Answer the password If it s nil it should default to an empty String password isNil iffrue password J password
18. needs A common idiom for organizing default parameters is to choose a priority order Create one method that defaults the most important parameter another which specifies that pa rameter but defaults the next most important and so on until you specify all parameters In the example above the destina tion for display is the most important parameter and the loca tion the next most important This approach limits the num ber of methods but ensures that the most commonly used combinations are available ABSTRACT SUPERCLASSES Some classes are not meant to be instantiated They exist only as repositories for interesting related bits of behavior The most powerful of these abstract superclasses reduce a set of re lated messages to one or two methods that each concrete sub class is required to implement Both Smalltalks provide Coll c tion as a good example If you create a subclass of Collection you need only implement do You get the rest of the enumera tion methods without further effort Identifying candidates for abstraction is not easy I got the following strategy for using this idiom from Ken Auer of Knowledge Systems If reusability is ever going to be an issue for a class divide it into two parts at the beginning an abstract part that contains only methods and few or no variables and a concrete part that holds the state necessary to actually com pute The example he used had an abstract FinancialInstrument and a concre
19. this way If you have the ob ject 10 and you add 5 to it you don t change 10 you get a new object 15 instead You don t have to worry about giving away your 10 and having it turn into a 15 behind your back Points and Rectangles are implemented much the same way After you have created a Point with Number gt gt all other opera tions translateBy return new Points Unfortunately Points can have their coordinates changed directly via x and y and Rectangles also offer methods for directly changing their values The simplicity of value objects comes at a price Their in discriminate use can result in excessive memory allocation If you must side effect an otherwise functional object do so only with a freshly allocated one in a small well defined scope preferably a single method As with all optimizations pillag ing a value object for speed should only be done when the THE SMALLTALK REPORT PRODUCT ANNOUNCEMENTS Product Announcements are not reviews They are abstracted from press releases provided by vendors and no endorsement is implied Vendors interested in being included in this feature should send press releases to our editorial offices Product Announcements Dept 91 Second Ave Ottawa Ontario K1S 2H4 Canada Object Technology International Inc OTI has announced a ma jor development agreement with International Business Machines Corpo ration The new agreement with IBM s Applications Busine
20. to the drawing and displaying them in a window Additional fea tures and functionality will be developed in future articles The focus is primarily on rendering graphics on screen so SmallDraw won t include such functions as saving drawings to files or printing to a printer GRAPHIC OBJECTS SmallDraw is a structured graphics editor as opposed to a bitmap editor In other words each figure drawn in the win dow is treated as a separate object Bitmap editors on the other hand work at the pixel level We can think of the main entity of the application as a drawing that contains several graphic shapes For simplicity we ll limit the set of two dimensional objects to LineSegment Rectangle Poly line Polygon and Ellipse Each graphic object will have attributes that describe its shape For instance a LineSegment can be described by a start point and an end point and a Polyline can be described by an ordered set of points All objects will have an inside color or none in which case it will appear to be hollow a border color and a line width A graphic object s behavior should in clude methods for accessing and modifying its attributes and for displaying itself at a given scale The following class hierarchy defines the graphic objects used in SmallDraw I ve prefixed each class name with SD to distinguish it as a SmallDraw object and to avoid any naming conflicts when filed in to an image Object SDGraphicO
21. HOW TO DEFINE CLASS INSTANCE VARIABLES Ordinarily users see a class definition in a browser like the example in Listing 1 After the code from this column is added to an image users will see an extended class definition in the browser The extended class definition consists of two messages one to the class and one to the metaclass Listing 2 is an example of an extended class definition with no class in stance variables The message argument to the metaclass is an empty string Adding a class instance variable is just like adding an in stance variable The user modifies the argument to the mes sage instanceVariableNames The argument is a string containing names of class instance variables Then the user saves the class definition through the menu The system redefines the class and recompiles as needed Listing 3 is an extended class definition with a class instance variable named defaultDirection IMPLEMENTING CLASS INSTANCE VARIABLES The code to add class instance variables to Smalltalk V Windows consists of five methods four of which are funda Listing Class Definition for AnimatedObject Object subclass AnimatedObject instanceVariableNames position oldPosition jumpIncrement direction goCount classVariableNames poolDictionaries WinConstants VoL 1 No 7 May 1992 mental and one that is a modification to the class hierarchy browser A complete listing of the code is included at the end of this
22. The Smalltalk Report The International Newsletter for Smalltalk Programmers May 1992 Volume Number 7 IMPLEMENTATION oF 0S 2 MULTI THREADING SUPPORT IN SMALLTALK V PM By Doug Barbour Contents Features Articles 1 Implementation of OS 2 Multi chreading Support in Smallealk V PM by Doug Barbour 7 SmallDraw Release 4 Graphics and MVC Part by Dan Benson Columns 13 Getting Real Class Instance variables for Smalltalk V by Juanita Ewing 16 The Best of Comp Lang Smalltalk More frequently asked questions by Alan Knight 19 GUls Separating the GUI from the application by Greg Hendley and Eric Smith 23 Smalltalk Idioms Why study Smalitalk idioms by Kent Beck Departments 25 Product Announcements 26 What They re Saying About Smalltalk malltalk V PM hereafter referred to as VPM is an excellent OS 2 applica tion development environment that provides most of the needed facilities especially in release 1 3 When combined with a third party window edit ing product such as WindowBuilder from Cooper and Peters applications can be created easily without the OS 2 Toolkit In a multitasking system such as OS 2 however complex applications frequently need to execute multiple tasks concurrently us ing system facilities This article explores the implementation of VPM and discusses how the non Smalltalk parts of an application can communicate with rhe Smalltalk parts
23. This new release supports two Smalltalk language implementations Smalltalk V Windows V1 1 for Windows 3 0 and Smalltalk V PM V1 3 for OS 2 Supported networks include Novell NetWare LAN Server and LAN Manager Configurations are available from three user systems up to site or special corporate licenses For further information contact Object Technology International Inc 1785 Woodward Drive Ottawa Ontario Canada K2C OP9 613 228 3535 Smalltalk will fuel the growth of many new idioms I am still collecting idioms If you identify one you would like to share contact me Kent Beck has been discovering Smalltalk idioms for eight years at Tektronix Apple Computer and MasPars Computer He is also the founder of First Class Software which develops and distributes re engineering products for Smalltalk He can be reached at P O Box 226 Boulder Creek CA 95006 or kenth maspar com 25 26 WHAT THEY RE SAYING ABOUT SMALLTALK Excerpts from industry publications Changing the way you develop software is a nontrivial decision You are not going to take seasoned FORTRAN or C programmers and turn them into Smalltalk wizards overnight You are likely how ever to find one or more programmers in your development group who are highly interested in object technology These self motivated early adopters are good candidates for a core transition team within your development group But they must be given training in obje
24. a end of February 1992 15 shipping W log C VOSS Windows 750 475 to end of February 1992 15 shipping pa Quantity discounts available Visa MasterCard and EuroCard accepted A R T S Logic Arts Ltd 75 Hemingford Road Cambridge England C51 3BY ao TEL 44 223212392 FAX 44 223 245171 15 VoL 1 No 7 May 1992 16 HE BEST OF comp lang smalltalk Alan Knight More frequently asked questions some of the frequently asked Smalltalk questions posted on USENET I must be off to a bad start be cause much of this column is taken up with additions and changes from last month s information I guess it s the price we pay for working in an area of rapid change First change I said there was no official list of frequently asked questions One has now been established and I ll be incorporating infor mation from it The list is maintained by Craig R Latta latta con berkeley edu and is available for ftp from xcf berkeley edu Many thanks to Craig for taking on the maintainer s job T month I continue describing and trying to answer MORE FREE STUFF Last issue I listed some sources of freely available Smalltalk code With a few exceptions most of that code comes in the form of small goodies These can be system enhancements bug fixes or utilities but are seldom large enough to be called applications This is only natural Many people are willing to freely contribute their own small fixes
25. al this is like world in world series for baseball We hope this helps clarify the issue and sincerely apologize for any confusion the posting may have caused Alan Knight is a researcher in the Department of Mechanical and Aerospace Engineering at Carleton University Ottawa Canada KIS 5B6 He currently works on problems related to finite element analysis in ParcPlace Smalltalk and has worked in most Smalltalk dialects at one time or another He can be reached at 1 613 788 2600 x5783 or by e mail as knight mrco carleton ca THE SMALLTALK REPORT UIs Greg Hendley and Eric Smith Separating the GUI from the application ry your garden variety Smalltalk application running under a GUI Of what major parts does it consist In most cases somewhere down in the depths is the Domain Model This is made up from classes that represent the real things users think they are manipulat ing e g transistors diodes connections etc All of these classes are commonly implemented to know as little about the user interface as possible Many would agree that ideally the domain model objects don t even know that such a thing exists This is all old hat and we ll assume that you re famil iar with the concept The other common component of a GUI based applic ation is not surprisingly the user interface Here is found all of the knowledge of what kind of widget is used to present which information where it
26. alled the Network Advisor ment environment for digital analog and The Network Advisor offers a compreben mixed mode printed circuit board testing sive set of tools including an expert system MIDLAND BANK Midland Bank built a Windowed Technical Trading Environment for currency futures and stock traders using Smalltalk V statistics and protocol decades to speed problem isolation The NA user interface is built on a windowing system which allows multiple applications to be executed simultaneously KEY FEATURES E World leading award winning object oriented programming system E Complete prototype to delivery system E Zero cost runtime E Simplified application delivery for creating standalone executable EXE applications E Code portability between Smalltalk V Windows and Smalltalk V PM E Wrappers for all Windows and OS 2 controls E Support for new CUA 91 controls for OS 2 including drag and drop booktab container value set slider and more E Transparent support for Dynamic Data Exchange DDE and Dynamic Link Library DLL calls E Fully integrated programming environ ment including interactive debugger source code browsers all source code included world s most extensive Win dows and OS 2 class libraries tutorial printed and on disk extensive samples Extensive developer support including technical support training electronic developer forums free user newsletter E Broad base of third pa
27. and favorite enhance ments to the community Ic takes a much greater commitment to contribute a large project Generally large projects come from university research projects LARGER SCALE APPLICATIONS The first of these is the T Gen parser generator package written by Justin Graver graver ufl edu at the University of Florida The package is described as a general purpose object oriented tool for the automatic generation of string to object translators and is available by ftp from bikini cis ufl edu The second item is a group of packages by Stephen T Pope and others related to the Smallmusic project This is a project to discuss and develop an object oriented system for music There is an electronic mailing list for discussions of the project and several implementations and documents If you have access to Internet electronic mail you can join the mailing list by sending a request to smallmusic request xcf_berkeley edu The implementations and documents are available by ftp from ccrma ftp stanford edu The most re cent implementation is called MODE not to be confused with the MoDE user interface toolkit available from the University of Illinois archive at st cs uiuc edu MODE runs under ParcPlace Smalltalk Release 4 0 and combines the functions of several earlier applications running under ParcPlace Smalltalk 2 X If you re used to commercial software it pays to be aware of a few differences when dealing with
28. bject insideColor borderColor lineWidth SDLineSegment start end SDPolyline vertices SDPolygon SDQuadrangle SDEllipse The common attributes of all graphic objects are collected in the superclass SDGraphicObject SDPolygon is identical to SD Polyline except its boundary is closed Rather than use Smalltalk s Rectangle class I defined a separate class with a more general name SDQuadrangle which inherits from SDPoly gon but is constrained to four vertices and 90 degree angles Representing a rectangle by an origin point and a corner point assumes it is always aligned with the x y axis A more general representation allows rectangles to be oriented at any angle I ve defined SDEllipse as a subclass of SDQuadrangle more for con venience of representation than semantics since an ellipse can be represented by its bounding rectangle and except for dis play it acts just like a quadrangle DISPLAYING GRAPHIC OBJECTS In Release 4 graphics are displayed on two dimensional graphic media all of which are subclasses of DisplaySurface With the three types of display surfaces Window Pixmap and Mask there are two approaches one can take display graphics directly on screen using a Window or display graph ics off screen using a Pixmap or Mask before final on screen presentation Off screen rendering can result in smoother looking updates and eliminate flashing but is a bit more in v
29. bjectworks Smalltalk development environment and a paral lel implementation of Versant Object Technology Corp s object database management system This will enable users to tap informa tion from legacy systems and convert it to objects Because the object oriented market is in its infancy Po Object won t generate any short term income As the object oriented mar ket becomes more mature however Sequent s early entrance will help it say analysts Sequent s software cure Gary Andrew Poole UNIX Woa_p 3 92 But we Microsoft also expected and predicted that OOP would become a vendor buzzword long before great OOP solutions were generally available Our concern was to ensure that the press did not treat OOP as an end in itself but merely as a means to make software easier to design and maintain for developers to make applications easier to use and more functional for end users If OOP does not provide these benefits then it remains only an acronym not a solution Our concerns about OOP being over sold however remain Object oriented tools and systerns are the most sophisticated and complicated of any software products ever built Object orientation is not something that can be tacked onto an existing system it must be designed in It is very difficult to do right technically And the focus must always remain on providing real value to the consumer Object insider Bill Gates OBJECT MAGAZINE 3 4 92 T
30. bleNames poolDictionaries AppcDLL methods createThread stackAddress stackSize stackSize notifyHwnd notifyHwnd lt api CREATETHREAD ulong ushort handle ushort gt self invalidArgument PM message Due to memory considerations only about the first 478 are mapped here Any message numbers received that are greater than the size of PMEvents are looked up in the global Dictionary PMEventsExtra The PM message number 558 for example is the key for this dictionary and the method name symbol is its value hmerror with Once the PM message has been mapped to a method name via either PMEvents or PMEventsExtra the PM message processing thread sends a Smallealk message to the appropriate window object using the two arguments provided by PM For more details look at any of the wm instance methods in the Window class EXTENSION OF THE VPM PM INTERFACE MODEL The existing VPM message interface with PM is extended to support communications with the additional thread This communication is carried out by having the thread create a PM message queue and passing its handle to the VPM envi ronment This handle is then used with the WinPostQueueMsg PM call to post messages to the thread One of the message parameters should be the handle of the notifier window that is to receive notification when the request is complete The thread performs whatever is requested and posts a PM mes sage to the notifier window See Figur
31. ch of the three layers is associated with a different level of code volatility Once a reasonably solid Model layer has been implemented it changes very little from version to version of the application The code in the Control layer of ten changes only a little more frequently Several more trials may be required to arrive at a solid Control layer but once ob tained it also changes little between versions It is usually ex tended rather than modified On the other end of the scale the presentation aspects of an application can change very rapidly These are more of ten modified than extended The presentation also bears the brunt of keeping up with changes in the host GUIs By sepa 21 22 a GUIs Listing 2 The Control layer Object subclass SystemLogonControl instanceVariableNames interface userName password model classVariableNames poolDictionaries emdCancel Command The only thing that happens here is tha the application closes up and goes away self interface close cmdLogon Command The user wants to log on We ll give it a try If we succeed then the application should close up and go away If we fail then the interface should confront the user with the problem self model verifyPassword self password forUser self userName iffrue self interface close ifFalse self interface notifyInvalid interface Answer the object which implements the interface layer
32. color to use and then what shape to dr aw SDPolygon for instance does the following displayOn aGraphicsContext scale aScalePoint pts pts self vertices collect p p aScalePoint self insideColor isNil ifFalse aGraphicsContext paint self insideColor displayPolygon pts self borderColor isNil ifFalse aGraphicsContext paint self borderColor lineWidth self lineWidth displayPolyline pts Note that the displayPolygon method displays a filled poly gon defined by the set of points whereas the displayPolyline method displays only the boundary GraphicsContext has similar methods for circular shapes as seen in the display method for SDEllipse displayOn aGraphicsContext scale aScalePoint bb bb self boundingBox scaleBy aScalePoint self insideColor isNil ifFalse aGraphicsContext paint self insideColor displayWedgeBoundedBy bb startAngle 0 sweepAngle 360 at 0 0 self borderColor isNil iffalse aGraphicsContext paint self borderColor lineWidth self lineWidth displayArcBoundedBy bb startAngle 0 sweepAngle 360 at 0 0 E SMALLDRAW RELEASE 4 GRAPHICS AND MVC THE MVC ARCHITECTURE Smalltalk applications are constructed using the Model View Controller MVC architecture A brief overview of the MVC paradigm will help in putting together our applica tion The process begins by dividing the application into two parts the information model the part that manages data storage
33. ct oriented analysis and design as well as Smalltalk programming Impor tant tip A Smalltalk programmer with a structured procedural mind set is not really a Smalltalk programmer Technology Smalltalk speaks to users needs Jim Salmons and Timlynn Babitsky Open Systems Topay 2 17 92 Practical studies based on function point analysis show that a 4GL solution to a typical problem is 50 simpler than 3GL solution but only 15 simpler than an OOPL solution This is probably because the OOPL s user defined types are counted while those built into the 4GL are not The size and complexity of a 4GL solution grows incre mentally with the system With an OOPL you just add components to meet each new challenge Fourth generation and other specialized languages will stick around if only for cultural reasons most of to day s programmers cut their teeth on them The world is unlikely to rally around a single OOPL Technical and financial developers use C MIS shops prefer Smalltalk or are waiting for object oriented Cobol Ironically object oriented 4GLs now accompany some OO databases to help them integrate objects from multiple OOPLs Software amp Systems Fourth generation heyday at an end Craig Hubley COMPUTING CANADA 2 17 92 At press time Sequent s Larry Evans didn t want to elaborate on Pox Object but according to documents obtained by UNIX WORLD the product will combine a parallel version of the Parc Place O
34. d by the forked process which causes the AppcNotifierWindow instance to be sent a vpmAppcThread Queue with message The vpmAppcThreadQueue with method makes a copy of the thread queue passed by the thread adds a thread QueveEvent to CurrentEvents and returns At this point VPM returns control to PM to allow other applications to perform windowing operations The forked process removes the threadQueueEvent from CurrentEvents and sends it to the AppeNotifierWindow instance The threadQueueEvent sends itself the event message with threadQueue as the argument The AppcNotifierWindow instance sends the registered method for the threadQueue event threadQueue to the owner the AppcConversation instance with itself as the argument The threadQueue method assigns the thread queue to an instance variable and signals the semaphore This allows the waiting main process to continue e The forked process is terminated by the threadQueueEvent method SUMMARY Using the concepts explored in this article interfaces may be written from VPM to any long running application without adversely affecting other applications running in the system H Doug Barbour is an Information Systems Engineer at Duke Power Company He is also a partner at Barbour Enterprises specializing in custom interfaces to Smalltalk V PM as well as general purpose classes Doug may be reached at Barbour Enterprises 1058 D Kelly Circle Cl
35. e 1 for a diagram of this interaction The first issue to be addressed is the selection of message numbers for communications with the thread A consecutive block of message numbers should be chosen for each applica tion avoiding conflicts Message numbers must be unique within one VPM image User defined message numbers must be greater than 4 096 to avoid conflicts with PM messages For the APPC interface message numbers range from 29 500 to 29 505 Each message number must have an entry in PMEventsExtra that specifies the method name associated with it For example message number 29 501 is associated with the vpmAppcVerbDone with method The message definitions used in the APPC interface are PMEventsExtra THE SMALLTALK REPORT Listing 3 Creating a subclass of auxiliary window to handle PM messages InvisibleNotifierWindow subclass AppcNotifierWindow instanceVariableNames vcbAddress threadQueue classVariableNames poolDictionaries InvisibleNotifierWindow methods threadQueueEvent Description A message has been received Cause the associated event to occur Role Private Parameters none Returns self self event threadQueue verbDone a Description A message has been received Cause the associated event to occur Role AsyncNotifier subclass AppcConversation instanceVariableNames appcLibrary notifierWindow threadStack threadQueue sem classVariab
36. eBox notify withText Logon Failed open The usual large method for opening all of the views Only the creation code for the important subpanes is included THE SMALLTALK REPORT Listing cont d addSubpane Entryfield new owner self framingBlock paneName userNameField startGroup tabStop when getContents perform getUserName when textChanged perform setUserName yourself addSubpane EntryField new owner self framingBlock paneName paswordField startGroup tabStop when textChanged perform setPassword yourself addSubpane Button new owner self framingBlock paneName okButton defaultPushButton startGroup tabStop when clicked perform bcOk contents Ok yourself in Listing 2 if the user requests the log on command the In terface will send the message cmdLogon to the control layer As can be seen in the method for this message above the con trol layer then packages up the information necessary for the model to validate the log on Should the log on be successful the control layer decides that the application is at an end and closes things up Otherwise it decides the user needs to be notified of the failure The actual notification is a presentation detail and is therefore left to the interface Admittedly this is a rather simple example However we have used the ICM arch
37. ed since it does not support OS 2 threads directly An additional OS 2 thread is the best way to solve this problem The only thing to be worked out is the means of communicating between VPM and the thread OS 2 pro vides many ways to accomplish multi thread communication using PM messages is the easiest and most robust way because PM messages are already used extensively in VPM To understand how to do this some background information is needed VPM IMPLEMENTATION VPM provides support for multitasking via the Process ProcessScheduler and Semaphore classes As long as all of the sub tasks of the application are strictly Smalltalk code this method works quite well Most VPM application developers don t care if this multipro cessing is simulated and does not actually use OS 2 s thread capability This fact becomes cuntanied un page 3 EDITORS CORNER John Pugh Paul White n the olden days one of Smalltalk s most notorious drawbacks was its inflexibility with respect to in terfacing with software developed in other languages Application Program Interfaces APIs offer a solucion to this problem allowing developers to interface easily with existing DLLs regardless of the language in which they were developed However as Doug Barbour points out in our lead article this month it is still not a perfect solution If Smalltalk is using a single thread processor it in effect locks up while waiting for a retum from an API call
38. eds much faster than if you always have to invent new mechanisms from scratch Standing on the brink of a new column I look forward to exploring the range of idioms available to Smalltalk programmers From time to time Ill be joined by prominent Smalltalkers who will describe their favorite idioms We will also explore the subtle differences between the Digitalk and the ParcPlace schools This column will present idioms at many levels of com plexity and scope Rather than present all 50 or so of the idioms I have identified so far 1 have chosen a smattering to get things going The first few are small in scale and likely to trip up programmers new to Smalltalk The con cluding design idioms are more likely to interest more advanced programmers VoL 1 No 7 May 1992 CONDITIONALS AS EXPRESSIONS In most procedural languages conditional statements do not return values In Smalltalk however the result of sending iffrue ifFalse to the Boolean true for example is the value of the last expression in the block which is the first argument This fact can be used to advantage to simplify some methods considerably While you could write result foo isNil iffrue result 5 ifFalse result 7 result It is shorter and after you get used to it easier to write result Tesult foo isNil iffmue 5 ifFalse 7 result Once you ve gone that far you can get rid of the temporary variable entirely and
39. enu bars There are several types of Wrappers beginning with the plain brown Wrapper no frills to the most decorative EdgeWidgetWrapper all the frills We ll use the EdgeWidgetWrapper so that we can have a menu bar but we ll need to turn off the vertical scroll bar as each EdgeWidgetWrapper comes with a vertical scroll bar by de fault aWrappedView EdgeWidgetWrapper on aSmallDrawView noVerticalScrollBar We can now place our wrapped view in the window by specifying it as a component of the ScheduledWindow aWindow component aWrappedView Our application will be invoked by first creating an in stance of SmallDraw and then asking it to open itself using the following SmallDraw instance method open aWindow aSmallDrawView aWrappedView aWindow ScheduledWindow new aWindow label SmallDraw aSmallDrawView SmallDrawView model self aWrappedView EdgeWidgetWrapper on aSmallDrawView noVerticalScrollBar aWindow component aWrappedView aWindow openWithExtent 200 200 This of course could be simplified to a single statement open ScheduledWindow new label SmallDraw component EdgeWidgetWrapper on SmallDrawView model self noVerticalScrollBar openWithExtent 200 200 Universal Database OBJECT BRIDGE This developer s tool allows Smalltalk to read and write to ORACLE INGRES SYBASE SQL DS DB2 RDB RDBCDD dBASEIII Lotus and Excel Intelligent System
40. es E GETTING REAL s i l e n c e w collection of tools tor preiert management and code delivery full multi user project management e source code version control e aulomatic change documenting release packaging ship compiled code without source e reconfigurable installation tool e change log browser and restorer code performance profiling 99 95 idigamma solutions P Unil 6 387 Spodina Avenue Toronto Onlusio Cenoda MST 2G6 Phane 416 aas 8833 Fux 416 408 2850 nion unli Marh 313 1992 n unti May Jsl 1992 1 no class instance variables This is necessary because the eval uation of a class definition in the browser must return the same result Class recreate numberOfExtraFields New This new private method is used to recreate the class object when the number of class instance variables has changed It deals with a number of implementation details such as storing the new class in the Smalltalk dictionary and the global vari able TableOfClasses and inserting the new class into the class inheritance hierarchy ClassHierarchyBrowser acceptClass aString from aPane Modified Listing 3 Extended Class Definition for AnimatedObject with a Class Instance Variable Object subclass AnimatedObject instanceVariableNames goCount position oldPosition jumpIncrement direction classVariableNames poolDictionaries WinConstants AnimatedObject class i
41. f input If it involves knowledge of the domain model or the relationships among the various pieces of information presented it belongs in this category ICM ARCHITECTURE Most standard Smalltalk application architectures of the past have had just two layers a model and an interface Using the approach presented here results in a three layer application We ll call this structure the Interface Control Model ICM INTERFACE LAYER All of the information pertaining directly to what shows up on the end user s screen is part of the Interface layer This includes the choice of display widgets colors fonts menus vs radio buttons as well as all of the first level input han dlers They should normalize the input so that the Control layer doesn t have to know what kind of screen widget it s coming from If you use a window builder of any kind for this compo nent you ll be done in minutes Except for the automatically generated methods used for setting up the various panes but tons etc nearly all of the methods given here will be one lin ers They just mediate between the GU independent world of the control layer and the very GUI dependent collection of user interface classes provided by Smalltalk CONTROL LAYER This layer is where all of the work involved in producing a high quality user interface ends up This is where selected items mean something and where the smarts to translate user commands into action on the do
42. feel like before you can write it And you can t afford to throw the prototype away when you re done With Smalltalk V you don t Start with the prototype There s no development system you can buy that lets you get a working model working faster than Smalltalk V Then incrementally grow the prototype into a finished applica tion Try out new ideas Get input from your users Make more changes Be creative Smalltalk V gives you the freedom to experiment without risk It s made for trial And error You make changes and test them one at a time Safely You get immediate feedback when you make a change And you can t make changes that break the system It s that safe And when youre done whether youre writing applications for Windows or OS 2 you ll have a standalone application that runs on both Smalltalk V code is portable between the Windows and the OS 2 versions And the resulting application carries no runtime charges All for just 499 95 So take a look at Smalltalk V today It s time to make that prototyping time productive Smalltalk V is a registered trademark of Digitalk Inc Other product names are trademarks or registered trademarks of their respective holders Digitalk Inc 9841 Airport Blvd Las Angeles CA 90045 800 922 8255 213 645 1082 Fax 213 645 1306 LOOK WHO S TALKING HEWLETT PACKARD NCR HP has developed a network trouble NCR bas an integrated test program develop shooting tool c
43. goes on the display and what happens when the end user does something to it Unfortu nately this part of most GUI based applications comes in a lump We ll cover how and why the UI component should be further divided When the user interface for a GUI based application is ex amined at least two broad categories of function can be found The most apparent we ll call for lack of a better term the interface The choice of display elements to be used falls into this category For example a certain set of choices may be offered as a list box set of radio buttons or pull down menu Other things in this category are the size and locations of such screen elements how they respond to user input what color they are what fonts they use and so on Anything per taining directly to presentation or the first or lexical level of user input handling belongs in this category The other broad category involves control of the applica tion The semantic components of an application belong in this category Examples include things like list B must be re freshed if the user makes a new selection from list A Other things that belong here are the handlers for the various com mands e g cut copy and paste available to the user or at least those that don t simply affect the display The control category contains all of the things that define what it means to be the application except for the last stages of presentation and the first stages o
44. hanged instanceVars isClass not Juanita Ewing is a senior staff member of Instantiations Inc a soft ware engineering and consulting firm that specializes in developing and applying object oriented software projects and is an expert in the de sign and implementation of object oriented applications frameworks and systems In her previous position at Tektronix Inc she was re sponsible for the development of class libraries for the first commercial quality Smalltalk 80 system Her professional activities include Work shop and Panel Chairs for the OOPSLA conference VOSS Virtual Object Storage System for Smalltalk V Seamless persistent object management with update transaction control directly in the Smalltalk language Transparent access to Smalltalk objects on disk Transaction commit roliback Access to individual elements of virtual collections and dictionaries Multi key and multi value virtual dictionaries with query by key range and set intersection Class restructure editor for renaming classes and adding or Temoving instance variables allows incremental application development Shared access to named virtual object spaces Source code supplied Some comments we have received about VOSS _ clean elegant Works like a charm Hal Hildebrand Anamet Laboratories Works absolutely beautifully excellent performance and applicability Raul Duran Microgenics Instruments VOSS 286 595 375 t
45. he cor troller s view This can be useful for animating objects being dragged between windows or for drawing objects that extend beyond a view s bounds but it can also possibly cause some confusion or give an impression of inconsistency since most other commercial applica tions do not behave that way PUTTING IT ALL TOGETHER In order to get our application to appear on the screen in its own window we use an instance of ScheduledWindow The Scheduled part of the name indicates that its instances are scheduled with ScheduledControllers the control manager With Release 4 ScheduledWindows take on the look and feel of the host windowing system of the specific platform on which it runs This applies to only the outer portions of the window such as the title bar close and zoom boxes The in terior of the window maintains the Objectworks Smalltalk look and will appear the same across all platforms Creating a ScheduledWindow and giving it a label that will appear in its ti tle bar is straightforward 11 VoL I No 7 May 1992 E SMALLDRAW RELEASE 4 GRAPHICS AND MVC aWindow ScheduledWindow new aWindow labet SmallDraw Now that we have a window that knows how to render it self on the screen we can All it wich our SmallDrawView How ever we must first place a Wrapper around the view Wrap pers add decoration to the views they contain such as color borders layout scroll bars and m
46. here is a creative tension building in the computer industry be tween the way we used to do it and the way we should do it Ob ject technology is causing this tension as the vision of the way we should do it clashes with current reality There is only one way to re solve this tension we find ourselves in either pull the vision of object technology towards reality or pull reality toward the vision Object Request Broker the end of the beginning Chris Stone OBJECT MAGAZINE 3 4 92 In the longer term it will be up to content specialists to define the basic services that classes should provide in a way that makes them more independent of their implementation context In addition to warranties and certification processes believe that class vendors should provide testing facilities with every class they ship Ideally these facilities would include a complete test bed for automatically sending a full range of messages to the class and check ing the correctness of its responses Providing developers with these testing tools would allow them to double check the performance of any class More importantly it would help them assure that any modi fications or subclassing they performed had not violated the basic functionality of the class Ultimately the solution to compensating class creators will be determined by market forces which usually have a way of defying the most well intentioned attempts at prediction
47. igitalk Inc 9841 Airport Boulevard Los Angeles CA 90045 310 645 1082 Digitalk Inc has announced that it is developing a 32 bit version of its Smalltall V development environment for UNIX to be delivered by year end The first platform for the company s new UNIX technology will be IBM s RS 6000 RISC Reduced Instruction Set Chip machine which runs AIX IBM s version of UNIX The new UNIX version of Smalltalk V is abased on Digitalk s 32 bit Smalltalk V technology for OS 2 2 0 Developers can develop their applica tions on either Smalltalk V for OS 2 or Smalltall V for Windows and these applications will run unmodified on the new UNIX release For more information contact Digitalk Inc 9841 Airport Boulevard Los Angeles CA 90045 301 645 1082 Object Technology International Inc has announced the immediate availability of its object oriented product development environment ENVY Developer R1 30 for Smalltalk V PM V1 3 and Smalltalk V Windows V1 1 This product provides a powerful concurrent software engineering en vironment for systems and applications development Team support ver sion control and configuration management are seamlessly integrated with Smalltalk V s programming environment Release 1 30 includes ENVY Packager OTI s tool for delivering small standalone Smalltalk applications Developers are provided with fine grained control over the inclusion and placement of objects included in the final product
48. irect access to the In ternet to conduct conversations without the delays of elec tronic mail Anyone on the Intermet can participate regardless of location The drawback is the requirement for a direct network connection meaning that the number of peo ple capable of participating is much lower than in electronic mail or USENET forums On March 3 Martin Brown mjb netcom com organized an IRC conference of Smalltalk users Even though it started at 8 30 p m Pacific Time making it awkward for eastern THE SMALLTALK REPORT North America and ridiculous for Europe the conference at tracted quite a few participants IRC runs almost exclusively on UNIX machines so almost all of the participants were Smalltalk 80 users A number of people from ParcPlace participated including VP Engineering Richard Dellinger and CEO Adele Goldberg Highlights in cluded a preview of features in the next ParcPlace release in beta test as I write and the opportunity to give feedback on features we d like to see in future versions It s hoped that this will be the first of many such conferences If you d like to participate in these conferences you will need an account on a machine with a direct Internet connec tion and a copy of the IRC program Contact your system ad ministrator for details LANGUAGE WARS Like so much about computers languages are a religious issue I won t say that this is especially bad for OOP languages but it s certai
49. itecture with very satisfying results to implement much larger and more complex applications Scalability is not a concern with this technique In fact as ap plications grow in size this sort of division becomes commen surately more important SEPARATING THE HOST GUI FROM YOUR APPLICATION Adding yet another layer to the all your Smalltalk applica tions may not sound just like what you were shopping for VoL 1 No 7 May 1992 addSubpane Button new owner self framingBlock paneName cancelButton startGroup tabStop when clicked perform bcCancel contents Cancel yourself openOn aModel Open me up on the given model self control model aModel self open setPassword aPane Generated by WindowBuilder for a pane callback The user has changed the password Tell control about the change self control password aPane contents setUserName aPane Generated by WindowBuilder for a pane callback The user has changed the user name Tell control about the change self control userName aPane contents However we re not making these suggestions just to get you to draw another box and arrow on all your slides There are at least three considerable advantages to the ICM architecture These advantages fall in the areas of maintenance project management and portability MAINTENANCE In our experience with implementing highly interactive appli cations ea
50. l is WindowBuilder Instead of tediously hand coding window definitions and rummaging through manuals you ll simply draw your windows and WindowBuilder will generate the code for you Don t worry you won t be locked into that first inevitably less than perfect design WindowBuilder allows you to revise your windows incrementally Nor will you be forced to learn a new paradigm WindowBuilder generates standard Smalltalk code and fits as seamlesaly into the Smalltalk environment as the class hierarchy browser or the debugger Until March 31st WindowBuilder V PM will be available at an introductory price of 295 100 off the list price of 395 WindowBuilder V Windows sells for 149 95 Both include an unconditional 60 day guarantee For a free brochure call us at 415 855 9036 or send us a fax at 415 855 9856 You ll be glad you did Phone 415 855 9034 Fax 415 855 9856 Compusenve 71571 407 The rectangle is rubber banded as long as the mouse button is pressed however the shape only needs to be updated when ever the mouse moves Creating the rectangle with the ver tex vertex method allows the rectangle on screen to be stretched in any direction from the initial corner point This is demonstrated below showing four different snapshots of rub ber banded rectangles superimposed on each other You may notice that the Screen instance method used for rubber banding applies to the entire screen and is not clipped to t
51. leNames poolDictionaries AppcRetumCodes AppcConstants CharacterConstants AppcConversation methods initialize appeLibrary AppcDLL open Private Parameters none Returns self self event verbDone vpmAppcThreadQueue mp1 with mp2 Description A PM message has been received Remember the parameter values add the message to CurrentEvents and return to PM as soon as possible Role Private Parameters mp1 PMLong first parameter from sender mp2 PMLong second parameter from sender Requires Instance Variables threadQueue Returns self a threadQueue mp1 deepCopy Listing 4 An example of application class self sendInputEvent threadQueueEvent vpmAppcVerbDone mp1 with mp2 Description A PM message has been received Remember the parameter values add the message to CurrentEvents and retum to PM as soon as possible Role Private Parameters mp1 PMLong first parameter from sender mp2 PMLong second parameter from sender Requires Instance Variables vebAddress Returns self vcbAddress mp1 deepCopy self sendInputEvent verbDone appcLibrary createThread threadStack asParameter stackSize 4096 notifyHwnd notifierWindow handle asParameter Fork a process to receive messages from the thread CurrentProcess makeUserIF Notifier run fork Wait for the vpmAppcThreadQueue with message sem wait Re establi
52. li cation Browser provides multiple views of a developer s application AM ST defines Smalltalk V applica tions as logical groupings of classes and methods which can be managed in source files independent of the Smalltalk V image An application can be locked and modified by one developer enabling other developers to browse the source code The source code control system manages multi ple revisions easily ope The original and still premier application manager for Smalltalk V ChangeBrowser As an additional tool available for Smalltalk V PM and Smalltalk V Windows Change Browser supports browsing of the Smalltalk V change log file or any file in Smalltalk V chunk format The addition of AM ST to the ImageSoft Family of software develop ment tools enhances and solidifies ImageSoft s position as The World s Leading Publisher of Object Oriented Software Development Tools VRDS 1 800 245 8840 ImageSeft Publisher of Develapment Tools All trademarks are the property of their respective owners ImageSoft Inc 2 Haven Avenue Port Washington NY 11050 516 767 2233 Fax 516 767 9067 UUCP address mcdhup image info continued from page I critical however when interfacing VPM to other products that will be called from a lower level language such as C The first thing to understand is how VPM uses OS 2 threads In VPM 1 3 two OS 2 threads execute when the en vironment is running a
53. ly the most significant development in software technology in 40 years Like all major baseline technology shifts this one won t be felt immediately but over a 10 year period A massive amount of development has to be done but this is so far reaching in its effects that it will impact lit erally everything that s being done with software You now have the VoL 1 No 7 May 1992 ability to standardize and that changes the economics of software development which is where the big bucks are spent Merrill Lynch amp Co s Anthony Pizi Multimedia is the future for training It allows people to learn at their own pace This technol ogy is very good for training people in a standardized way A firm s staff might be spread out among five different offices but they can all use the same training program Investment bankers might use multi media to give a presentation to a client and make changes on the fly But one of the biggest problems is portability You need either tremendous amounts of memory or a U haul to lug all the hardware like CD player CPU and monitor Live video is on its way but any time you incorporate video and sound huge files are created which have to be compressed More affordable boards are coming out so end users don t have to worry about losing any data Andersen Consulting Financial Markets Industry Group s Robert Gach Rule based processing and object oriented devel opment are tech
54. main model live The amount of thought that goes into this level will make or break your user interface The Control layer receives messages from the Interface layer that inform it about what the user is doing Some of these messages identify selection of options or objects Others notify the Control layer of the users request that a command be executed The Control layer in tum sends messages to the Interface layer to tell the interface what information is out of date e g updateListA Though the Control layer knows that the Interface layer exists has a pointer to it and even knows a few messages it can send it it does not by any means know everything The Con trol layer should send only a very limited set of messages to the Interface layer The Control layer should not even be aware of what class or classes the objects in the Interface layer are 19 VoL 1 No 7 May 1992 20 DOMAIN MODEL LAYER As mentioned above the good old Model layer is a well beaten horse It should suffice to say that objects living down here know little or nothing about the fact that they even have an interface They may if they re nice notify unknown ob jects above when important information has changed ISOLATION An important aspect of the ICM approach to application de sign is that the lower layers have as little knowledge about the layers above them as possible They communicate only via a carefully designed protocol The Model laye
55. mple application To continue the example shown oystem Logon Figure 1 User name Password Requestor m GUIs Listing An implementation of the user name password requestor WindowDialog subclass SystemLogonDialog instanceVariableNames control classVariableNames poolDictionaries WBConstants beCancel aPane Generated by WindowBuilder for a pane callback Button Command Tell control that the user has chosen the cancel command self control cmdCancel bcOk aPane Generated by WindowBuilder for a pane callback Button Command Tell control that the user has chosen the logon command has been chosen My button says Ok but control and I have agreed that this represents the logon command self control cmdLogon control Private Answer the object who represents the control layer control isNil iffrue control self defaultControl control defaultControl Private Answer the default value for control self defaultControlClass new interface self defauttControlClass Private Answer the class of my default control layer SystemLogonControl getUserName aPane Generated by WindowBuilder for a pane callback Ask control for his idea of what the user name is aPane contents self control userName notifyInvalid Sent only by my control layer Tell the user that his log on failed Messag
56. n be instantaneously ported to an Intel board machine running Smalltalk V PM Action V 1 3 for Smalltalk V PM is now available directly from Ex perTelligence For more information contact ExperTelligence Inc 5638 Hollister Avenue Suite 302 Go leta CA 93117 805 967 1797 Digitalk Inc the developer of the Smalltalk V object oriented program ming system and a member of the IBM International Alliance for AD Cycle today announced the acquisition of Instantlations Inc Instantiations provides a wide range of services to Fortune 500 companies that are de veloping applications using Smalltalk object oriented technology Instantiations led by object technology veteran Michael Taylor is com performance of the finished applications is a problem for real users never on mere speculation CONCLUSION A good grasp of Smalltalk s many idioms can speed assimila tion of the language and its class libraries improve the pro ductivity of new development and accelerate understanding of legacy code This article has only scratched the surface of known Smalltalk idioms all of which were present in Smalltalk 80 as it escaped from Xerox The dispersion of VoL 1 No 7 May 1992 posed of some of the industry s leading object technology experts Principal among these are Allen Wirfs Brock a well known Smalltalk expert and Rebecca Wirfs Brock noted author and object oriented design methodologist For further information contact D
57. n merely draw objects in the window Future articles in the series will extend the function ality of SmallDraw We ll add selection translation scaling alignment using a DialogView and grouping of objects ver tical and horizontal scrolling of the view a cut copy paste clipboard and support for command keys Dan Benson is a Ph D candidate in the Department of Electrical En gineering at the University of Washington where he is developing a 3 D spatial database for human anatomy using Smalltalk and the Gem Stone OODBMS He may be contacted at Department of Electrical Engineering FT 10 University of Washington Seattle WA 98195 by phone at 206 685 7567 or email benson ee washington edu THE SMALLTALK REPORT ETTING REAL Juanita Ewing Class instance variables for Smalltalk V and class instance variables on class reusability and con cluded that classes implemented with class instance vari ables are more reusable than classes implemented with class variables Smallralk 80 derived versions of Smalltalk have class instance variables but Smalltalk V versions do not This column contains the code to add class instance variables to Smalltalk V Windows All objects in Smalltalk V have instance variables even class objects The code in this column just makes the facility apparent for classes and allows users to define new class instance variables n my last column I described the effect of class variables
58. nded to be is pointless To their credit many of the better known figures includ ing those closely associated with a particular language have tried to defuse this sort of partisanship There have been many patient explanations of the reasoning behind language fea tures and calm appeals to not try to use one tool for every job Occasionally though you have to fight sarcasm with sarcasm and I d like to reproduce a particularly good example which appeared in comp lang eiffel An announcement had been posted for the Tenth Eiffel User Conference to be held in Dortmund Germany John THE BEST OF COMP LANG SMALLTALK GDP Plan ahead for the largest object oriented conference and exhibition on the East Coast in 1992 THE NATIONAL CONFERENCE AND EXHIBITION JUNE 1 5 1992 THE SHERATON NEW YORK For a detailed brochure call 212 274 9135 or Fax 212 274 0646 Nagle nagle netcom com commented This is the TENTH conference And still nobody uses it Maybe there s something wrong Bertrand Meyer bertrand eiffel com who invented the Eiffel language responded A small clarification may be useful here As Mr Nagle so competently points out almost no one uses Eiffel in fact until recently there were only nine users But now a tenth person just started so we are holding a confer ence appropriately titled the TENTH EIFFEL USER conference to celebrate The new user is in Canada hence the word inter nation
59. nly no better than average Many of the people on the net are reasonable unprejudiced and willing to accept differences of opinion Unfortunately a lot of them aren t and they seem to be the ones who enjoy long debates on the relative merits of different languages Which language they are attacking or defending doesn t make too much difference Each community has its own points of snobbery and defensiveness Smalltalk advocates like to talk about pure OOP languages and about being one of the original sources of OOP They become very defensive when anyone calls their language slow or academic C advo cates like to talk about running fast and being the most popu lar language They get defensive when their language is called impure or a hack Eiffel advocates like to talk about soft ware engineering principles in a pure OOPL They get defen sive about being called obscure or proprietary There is some substance under the rhetoric mostly concentrated in a few basic issues MULTIPLE INHERITANCE Many current OOP languages make extensive use of multi ple inheritance Users of these languages tend to consider it an important part of OOP and naturally ask why Smalltalk is so backward as to not support it From the perspective of many in the Smalltalk community multiple inheritance has been tried and judged more trouble than it s worth Besides if you really want it you can always write it yourself
60. nologies that firms on the Street could use to steer clear of large applications which have millions of lines of code and don t lend themselves to flexible new product development Ob ject oriented technology and maximizing code reusability changing something copying it or adding a variant as opposed to starting from scratch would save the Street a lot of development costs and time Applications would get to traders faster if programmers could reuse packets of logic that are two to three commands long Appli cations with only 30 to 40 of the code are easier to maintain document understand and fix In addition by using both these technologies programmers stay in the end user s world and define systems from a business standpoint Hot technologies for the 1990s Ann Goodman and Jenna Michaels WALL STREET amp TECHNOLOGY 2 92 Computer Associates Dominique Laborde The industry is beginning to pay attention to object oriented programming IBM does not have any products in this category but needs to say something about an object oriented DBMS So the company pub lished a broad list of specifications Right now those specifications are not mature enough for us or anyone else to support Data access solution now has IBM road map Paul Korzeniowski SOFTWARE MAGAZINE 2 92 The constant refrain heard among the audience at PC Forum was this We shouldn t talk about objects because nobody agrees what the
61. nstanceVariableNames defaultDirection This method has been modified to update the reference to the selected class after saving a new definition of a class If the number of class instance variables has changed then a new class object will be created and the browser needs to be up dated This is a private method COMPLETE LISTING MetaClass class subclassOf aClass Private Answer a new metaclass that is a subclass of the metaclass for aClass newMeta newMeta self new newMeta assignClassHash structure aClass class structure superclass aClass Class iffrue Class ifFalse aClass class methodDictionaries Array with MethodDictionary newSize 2 newMeta superclass methodDictionaries newMeta MetaClass instanceVariableNames stringOfInstVarNames Define or redefine the set of class instance variables for the class which is an instance of this metaClass The number of class instance variable may be increased only if there are no existing instances of the class theClass oldSize newSize aStream theClassName theClass self instanceClass theClassName theClass symbol oldSize self instVarNames size newSize stringOfinstVarNames asArrayOfSubstrings size oldSize lt newSize iffrue if the size of the class object needs to increase there must be no instances theClass withAllSubclasses do aClass aClass allInstances notEmpty iffrue self error Has i
62. nstances self instVarNames stringOfInstVarNames oldSize lt newSize iffrue theClass recreate newSize oldSize _ recreate the class object theClass Smalltalk at theClassName aStream WriteStream on String new 64 theClass fileOutOn aStream Smalltalk logSource aStream contents forClass theClass self compileAll self allSubclasses do aClass aClass compileAll theClass Class fileOutOn aStream Append the extended class definition message for the receiver to aStream Include the statement for the definition of class instance variables THE SMALLTALK REPORT aString aStream cr nextPutAll self superclass printString space nextPutAll self kindOfSubclass space nextPutAll name storeString cr space space self isBits iffalse aStream nextPutAll instanceVariableNames aString self instanceVariableString isEmpty ifFalse aStream cr nextPutAll aStream nextPutAll aString storeString cI space space aStream nextPutAlL classVariableNames aString self classVariableString isEmpty ifFalse aStream cr nextPutAll aStream nextPutAll aString storeString Cr space space nextPutAll poolDictionaries aString self sharedVariableString isEmpty ifFalse aStream cr nextPutAll aStream nextPutAll aString storeString Include class instance variable definition aString self class instanceVa
63. olved so we ll stick with on screen rendering for SmallDraw From an object oriented point of view it seems reasonable to have the graphic objects display themselves since they should know best how to do that However we should not ex pect these objects to know Bresenham s line drawing algo VoL 1 No 7 May 1992 rithm or how to tum on a red pixel etc The object that deals with these primitive operations is an instance of GraphicsCon text Each instance of a display surface has its own graphics context that keeps track of parameters such as line width color font clipping rectangle etc The graphics context ob ject acts as the intermediary between objects to be displayed and display surfaces It maintains its local origin for its display surface and can display everything from images to text to ge ometric shapes The GraphicsContext instance methods for displaying geo metric shapes include line segments polylines filled polygons rectangular borders filled rectangles arcs and wedges filled arcs It is through these methods that the SmallDraw graphic objects are able to display themselves In SmallDraw when an object is asked to display itself it is sent an instance of a graphics context along with a Point that specifies the scale to be used Where applicable each type of object draws its inte rior if it has an inside color and then its border if it has a border color It will first tell the GraphicsContext what
64. over SC 29710 or by phone at 803 222 1363 THE SMALLTALK REPORT SMALLDRAW RELEASE 4 GRAPHICS AND MVC By Dan Benson raphics often play a big role in Smalltalk applica tions but it is also one of the more difficult areas to grasp This is particularly true of the current version of Objectworks for Smalltalk 80 Release 4 Even experienced users familiar with version 2 5 can be just as confused as newcomers to Smalltalk because cf the major changes in the way graphics is handled One reason for this confusion is the lack of adequate in depth explanations in the users manuals that come with Objectworks You will be pleased to know that this will soon be remedied by new chapters scheduled for the next release from ParcPlace Another source of confusion is that there are few examples from which to learn This series will de scribe a simple graphics application that might be instructive for those trying to get a better grip on Release 4 graphics and the MVC architecture What better way to experiment with rendering graphics than to build a structured graphics editor Commercial draw ing programs are now commonplace and many are quite so phisticated We ll borrow some ideas from these applications but will keep things simple Since we re using Smalltalk let s call our application SmallDraw We ll start off with a minimal version of SmallDraw We ll limit its capabilities to adding new graphic objects
65. ppc methods are exe cuted on behalf of the PM message processing thread They copy the message parameters to instance variables if necessary and add the message event to CurrentEvents via the sendInput Event method The return from a vpmAppe method causes VPM to return control to PM allowing other applications to perform window operations A REAL EXAMPLE Let s trace through a complete interaction sequence between VPM and the thread The interaction of interest is the thread notifying VPM that is has created its message queue and pass ing the queue handle as a message parameter This is imple mented in the initialize instance method of the AppcConversa tion class and is shown in Listing 4 Here are the steps e The instance of AppcDLL is created The instance of AppeNotifierWindow is created and the threadQueue event is registered e A VPM Semaphore instance is created to allow waiting until the thread has been created The thread s stack area is allocated as an instance of PMAddress The thread is started by sending the createThread stack Size notifywnd message to the AppeDLL instance e A VPM process is forked to wait for the thread to respond with the VPM_APPC_THREAD_QUEUE message The main VPM process waits for the semaphore to be sig naled thus causing the application to wait without dis turbing PM operations When the thread posts the VPM_APPC_THREAD_QUEUE mes sage it is processe
66. r good software engineering The argument asks What if your air traffic control system pops up a does not understand dialogue in the middle of a forced landing They also argue that strong typing enforces better design principles Almost as an afterthought they add that it makes programs run faster On the other hand Smalltalk Objective C and other ptogrammers argue that at least with current technology static typing systems either excessively restrict what pro grams can be written or else don t really eliminate the possi bility of run time type errors Further the errors that it catches are mostly those that would be trivially detected in testing Better to worry about what happens when your air traffic control system divides by zero Further they argue the flexibility chat you lose with static typing inhibits reuse and makes programming harder In a lot of languages static typing is also intimately bound up with multiple inheritance In languages like C and Eif fel variables can have values of different types but only if all of those types are subclasses of the declared type of that vari VoL 1 No 7 May 1992 17 18 Smallitalk V users the tool for maximum productivity fxsiArn me n Put related classes and methods into a single task oriented object called application Browse what the application sees yet easily move code between it and external environment Automatically document code
67. r knows virtually nothing about the application The Control layer knows all about the model but very little about the Interface layer It knows that it has an interface and knows a few messages it might send it e g updateListA The Interface knows nothing at all about the Model layer and only a little about the Con trol layer For example it knows what messages to send to the Control layer when the user has selected something or re quested that a command be executed A QUICK EXAMPLE IN SMALLTALK V PM Listing 1 provides a quick example of some of the principles we ve just discussed It is an implementation of the user name password requestor shown in Figure 1 The first class im plements the Interface layer When the user executes a command for example presses the Ok button to execute the log on command the inter face does nothing more than tell the control layer that the user has chosen that command At this point the Interface layer is not even aware that the operation might result in a failure Though the interface will be responsible for informing the user of such a failure see the method for notifyInvalid in Listing 1 it does not know where the failure occurs Note that none of the application state is maintained in the Interface layer The current values for the user name and password are all kept in the Control layer as shown in Listing 2 The class SystemLogonControl implements the control layer for our exa
68. re sulting combination of the two menus Determining the responsible party of a menu selection re quires the controller and view to keep track of the selectors each responds to When the SmallDrawController obtains the user s menu selection it asks itself whether the menu selec tion is one of its local menu items If so it responds to the se lection If not it asks its view the same thing If so the view is asked to perform the selection otherwise the model is asked to perform the selection RUBBER BANDING A common technique for drawing shapes interactively on screen is to use rubber banding Through rubber banding figures appear to be stretched into shape as the cursor moves across the screen For this to happen effectively the rubber band lines must be alternately drawn and erased in rapid suc cession without damaging the existing contents of the screen There are different ways to accomplish this in Smalltalk the simplest is to use the following Screen instance method displayShape shape lineWidth LineWidth at aPoint forMilliseconds milliseconds where shape Array of points defining the rubber band line s lineWidth width of line s to be drawn aPoint origin for shape in screen coordinates milliseconds length of delay before erasing Depending on the length of delay used the lines can ap pear to shimmer as they are quickly drawn and erased indicat ing their temporary or dynamic status From my expe
69. riableString aStream nextPut cr aStream nextPutAll self class name aStream nextPutAll instanceVariableNames aStream nextPutAlL aString storeString aStream cr space space Class Tecreate numberOfExtraFields Private Replace this class object with an identical object with additional fields for class instance variables newInstance mySuperclass myName oldid myName self symbol newlnstance self class basicNew oldid self id 1 to self class instSize numberOfExtraFields do i newlnstance instVarAt i put self instVarAt i mySuperclass self superclass mySuperclass removeSubclass self mySuperclass addSubclass newInstance Smalltalk at myName put newInstance newlnstance methodDictionary do Em m classField self iffme m classField newInstance newlnstance subclasses copy do sub sub superclass newlnstance sub recreate numberOfExtraFields TableOfClasses at oldId 1 put newInstance newlnstance id oldId self become DeletedClass ClassHierarchyBrowser acceptClass aString from aPane Private Accept aString as an updated class specification and compile it Notify aPane if the compiler detects errors result isClass result Compiler evaluate aString in nil class to nil notifying aPane ifFail true Smalltalk logEvaluate aString isClass result isKindOF Class isClass iffrue selectedClass result self c
70. rience this technique is very effective on a Macintosh but depending on the background color of the window it can be difficult to see on the IBM RS 6000 platform I don t know the quality of its visual appearance on other platforms I ve found that a line width of 1 and a 25 millisecond delay works well on a Macin tosh IIfx Since several methods make use of rubber banding and it may be necessary to modify these parameters for differ ent platforms the following SmallDrawController instance methods are defined rubberBandLineWidth 1 rubberBandDelay 25 Let s take a look at a very common rubber banding shape the rectangle For now this shape will be used in drawing SDQuadrangles and SDEllipses but eventually we ll use it for se lecting groups of objects in the window For this reason we define it as a separate SmallDrawController instance method called rectangleFromScreen Rectangles will be drawn on screen by pressing the mouse button which defines one corner of the rectangle dragging the mouse across the screen and releasing the mouse button at the opposite comer of the rectangle When the method is entered it will be assumed that the mouse button has just been pressed The method s job is to rubber band a rectangular shape from that comer point to the cursor point as it is being dragged across the screen The THE SMALLTALK REPORT __ this is a potent rapid application development tool which should
71. rom its words While learning Smalltalk a task that continues daily I have often been puzzled by a fragment of code Only upon reflection do I understand the author s intent About a year ago I began collecting examples of idioms I en countered and asked my friends to tell me about ones they found This article is an introduction to the material I have collected Many programmers new to Smalltalk spend most of their time just reading code Studying idioms can accelerate this process Knowing what to expect or at least having some where to turn when you are baffled by a piece of code is im portant to new Smalltalkers Another meaning for idiom is a style of speaking of a group of people As with spoken language Smalltalk has several di alects The two most prominent are the Digitalk and Parc Place dialects There were also two distinct Tektronix di alects easily distinguished from one another Xerox Special Information Systems the Analyst folks also had their own distinctive style New offshoots arise anywhere Smalltalk has taken root for several years Being conscious of the collective idiom of a body of code can also help more advanced programmers Code that ad heres to a shared idiom is easier to maintain as there are fewer gratuitous surprises for new readers Idioms also speed development through a kind of pattern matching process Once you have identified a circumstance in which an idiom is applicable coding proce
72. rty support including add on Smalltalk V products consulting services books user groups This Smalltalk V Windows application captured the PC Week Shootout award and it was completed in 6 hours Smalltalk V PM applications are used to develop state of the art CUA compliant applications and they re portable to Smalltalk V Windows
73. s Inc l 506 N State Street Ann Arbor Mi 48104 313 996 4238 313 996 4241 fax 12 Now to start the SmallDraw application we simply do the following SmallDraw new open Incidentally if we wanted our application window to have more than one subview we would need to place our views in an instance of CompositePart which would then be made the component of our window CompositeParts can contain any number of views or other CompositeParts Relative and absolute placement of subviews within composite parts is specified through Layouts The following SmallDraw instance method opens a window containing two SmallDrawViews each occupying half of the window vertically openWithTwoViews window composite window ScheduledWindow new label SmallDraw composite CompositePart new window component composite composite The left hand view add EdgeWidgetWrapper on SmallDrawView model self noVerticalScrollBar in LayoutFrame new leftFraction 0 TightFraction 0 5 topFraction 0 bottomFraction 1 The right hand view add EdgeWidgetWrapper on SmaltlDrawView model self noVerticalScrollBar in LayoutFrame new leftFraction 0 5 rightFraction 1 topFraction 0 bottomFraction 1 window openWithExtent 200 200 CONCLUSION In this article I ve presented a structured graphics editor SmallDraw albeit a minimal version I admit it s not much of an editor yet since the user ca
74. sh the main process as the receiver of PM messages CurrentProcess makeUserIF threadQueue anAppeNotifierWindow notifierWindow AppcNotifierWindow new open when threadQueue perform threadQueue when verbDone perform verbDone yourself sem Semaphore new threadStack PMAddress copyToNonSmalltalkMemory ByteArray new 4096 Create the external thread VoL 1 No 7 May 1992 Remember the thread s queue handle threadQueue anAppcNotifierWindow threadQueue Signal the main process that the message has been received sem signal Terminate the message receiver process Processor terminateActive at 29501 put vpmAppcVerbDone with at 29503 put vpmAppcThreadQueue with To create an additional thread from the VPM environ ment a DLL must be created to issue the DosCreateThread OS 2 call and to contain the code to be executed by the thread In Listing 1 the CreateThread function performs this action Pa rameters to CreateThread are the stack area to be used by the new thread the size of the stack area and the window handle to be notified when the thread is created and ready for work The stack is passed to the thread from the VPM environment to ensure that it is properly freed after thread termination The code in the Thread function initializes PM and creates a message queue It then posts the VPM_APPC_THREAD_QUEUE mes sage to the AppcNotifierWindo
75. simply write foo isNil iffrue 5 ifFalse 7 and AND or VERSUS amp AND There are two methods each for conjunction and disjunction in Smalltalk and and amp both return true only if both the re ceiver and the argument are true and or and both return true if either the receiver or the argument are true The differ ence is that the keyword versions and and or take a block as an argument rather than a Boolean The block is evaluated only if the result of the message is not determined by the re ceiver For instance you should use the keyword version of conjunction if evaluating the argument would cause an error if the receiver was false For instance if you wrote anArray size gt 10 amp anArray at 10 isNil you would get an ertor if anArray held less than ten elements In this case you would use the keyword version anArray size gt 10 and anArray at 10 isNil 23 24 E SMALLTALK IDIOMS This way the at message is not sent if anArray is too small The Objectworks Smalltalk release 4 image uses or to deter mine if operating system resources such as pixmaps that do not survive over snapshots need to be reinitialized It is com mon to see code like this pimmap isNil or pixmap isOpen not iffrue pixmap Pixmap extent The other reason to use the keyword versions is for opti mization If the second part of a conjunction is expensive and the receiver is often false u
76. sing and instead of amp can result in a considerable savings Why would anyone ever use the binary message versions of conjunction and disjunction Style baby The keyword versions often introduce extra parentheses as in the pixmap example above They use far more characters And since they are a little unusual they require a moment of thought every time you encounter them DEFAULT PARAMETERS Many programming languages provide the ability to not spec ify certain parameters for a procedure call and have them set to a default value Smalltalk provides this facility through a programming idiom A displayable object for instance might implement a message display as follows display self displayOn Display which in tum is implemented as displayOn aDisplayMedium self displayOn aDisplayMedium at 0 0 and so on until all the parameters needed to display the object have been collected As the user of this object you can specify as many or as few parameters as you need to get the job done The downside of implementing default parameters this way is the combinatorial explosion in the number of methods that can result If you are creating default parameters for a method that has five parameters you could potentially create 5 120 different methods If you write all the possible combinations you obscure the purpose of the original method If you don t write them all you run the risk of not providing the combina tion that someone
77. ss Systems ABS will enhance the use of graphical user interfaces and objects in ap plication development ABS will work with OTI a leading object oriented developer to cre ate an object oriented environment for developing cooperative applica tions OTI will combine the object oriented ENVY Developer technology with AS 400 cooperative processing support to provide a client server ap plication development environment for Smalltalk V programmers Smallralk V is an object oriented development language provided by AD Cycle International Alliance Member Digitalk Inc This new development agreement is intended to enhance the capabili ties of AS 400 programmers using graphical user interfaces cooperative programming and object oriented programming For more information contact Object Technology International Inc 785 Woodward Drive Ottawa Ontario Canada K2C OP9 613 228 3535 ExperTelllgence has announced a new version of its intelligent interac tive graphical application development system Actiont for version 1 3 of Digitalk s Smalltalk V PM The new version extends Action V1 2 It adds new CUA 91 objects like the Spin Button and the Slider It also gives more control to developers with the powerful Properties Editor and Coordinate Windows Finally it al lows interface compatibility with the Macintosh Lisp versions of Action Using Action an interface developed in Macintosh common Lisp or Procyon common Lisp on a Macintosh ca
78. t column Juanita Ewing described the differences between class variables and class in stance variables and lamented the fact that Smalltalk V does not provide class instance variables This month she provides an implementation of such a facility for V Finally Alan Knight provides us with his monthly round up of the Smalltalk bulletin boards The Editors The Smalltalk Repor ISSN 1056 7976 is published 9 times a year every month except for the Mar Apr July Aug and Nov Dec combined issues Published by SIGS Publications Group 588 Broadway New York NY 10012 212 274 0640 Copyright 1992 by SIGS Publications Inc All rights reserved Reproduction of this material by electronic transmission Xerox or any other method will he created as a willful violation of the US Copyright Law and is flatly prohibited Material may be reproduced with express permission from che publishers Mailed First Class Subscription rates 1 year 9 issues domestic 365 Foreign and Canada 90 Single copy price 8 00 POSTMASTER Send address changes and subscription orders to THE SMALLTALK REPORT Subscriber Services Dept SML P O Box 3000 Denville NJ 07814 Submit articles 10 che Editors at 91 Second Avenue Ottawa Ontario K1S 2H4 Canada THE SMALLTALK REPORT ImageSeft Asis developed by the SoftPert Systems Division of Coopers amp Lybrand enables the developer to manage large complex object orient ed applications The AM ST App
79. te Bond As you go along only allow state to move into the superclass if you can t reasonably put it in the sub class By pushing implementation decisions state down to the concrete class you have a better chance of finding what is truly common to the implementation of all such objects by examining what is left in the abstract superclass Another strategy for finding abstract superclasses comes from Ward Cunningham He suggests beginning an imple mentation without using inheritance at all Only when you get tired of manually copying and pasting methods from one class to another do you factor their commonality into a super class for both This strategy has the advantage that it identi fies commonality from concrete examples The best use of inheritance for code sharing is often not apparent until far into the design VALUES MASQUERADING AS OBJECTS One of the glories of objects is the ease with which they can be passed around But this easy mobility can become a nightmare if you have passed off an object and it begins to change with out your knowledge There is a suite of idioms for dealing with these aliasing problems The one described here is the simplest but it can have the greatest performance impact If once you have created an object you never change its state you cannot possibly have aliasing I call objects used in this way values because of their similarity to numbers In fact numbers in Smalltalk are implemented in just
80. ts and is the co inventor with Ward Cunningham of the popular Class Responsibility Collaborator CRC methodology for kick starting the design of object oriented systems Kent s column will identify Smalltalk idioms the coding pattems or mechanisms used frequently by experienced Smalltalk programmers in well defined situations but seldom written down or explained anywhere If you have ever looked at existing Smalltalk code and wondered Why is it done this way Kent may have the answer Experienced Smalltalk programmers are well aware of the virtues of separating the model from the user interface when developing GUI applications In this month s GUI column Greg Hendley and Eric Smith propose using a three layer approach Interface Control Model or ICM that fur ther separates the UI component into an interface layer and a control layer Simplistically you can think of the interface layer as the code that would normally be generated by a window builder and the control layer as the code that would respond to user interface interactions Why separate inter face from control As Greg and Eric point out one compelling reason is the speed with which sys tems can be ported across different hosts The interface component largely isolates the code specific to the host GUI from the portable control component As a result only the interface component need be ported They illustrate the approach by building a simple log on dialog In her las
81. very possible Non Smai ta THREAD Smauitan V PM Environment Appuication Class WrPostMessaceQueue WinGerMse Figure VPM communication with PM through additional OS 2 thread Listing Creating OS 2 threads define FUNCTYPE pascal far _loadds define VPMAPPC_THREAD_QUEUE 29503 define VPMAPPC_STOP_THREAD 29504 Function protoypes SHORT FUNCTYPE CreateThread BYTE stack USHORT stackSize HWND hwnd VOID FUNCTYPE Thread Global variables PBYTE stkbot SHORT rc TID threadID 0 HWND notifyHwnd HAB hab HMQ hmg Individual Functions SHORT FUNCTYPE CreateThread BYTE stack USHORT stackSize HWND hwnd notifyHwnd hwnd stkbot amp stack stackSize 1 J rc DosCreateThread PFNTHREAD Thread amp threadID VOID FAR stkbot return rc J VOID FUNCTYPE Thread l QMSG qmsq hab Winlnitialize NULL Initialize PM hmq WinCreateMsqQueue hab 0 Create application msg queue WinPostMsg notifyHwnd VPMAPPC_THREAD_QUEUE MPFROMLONG hma OL WinGetMsgq hab amp qmsg HWND NULL 0 0 while qmsg msg VPMAPPC_STOP_THREAD code to process each message WinGetMsgq hab amp qmsg HWND NULL 0 0 WinDestroyMsgQueue hmg WinTerminate hab E OS 2 MULTI THREADING SUPPORT Listing 2 The AppcDLL class DynamicLinkLibrary variableByteSubclass AppcDLL classVaria
82. via modifiable templates Keep a history of previous versions restore them with a few keystrokes View class hierarchy as graph or list Print applications classes and methods in a formatted report paginated and commented File code into applications and merge them together Applications are unaffected by compress log change and many other features CodeIMAGER V286 VMac 129 95 VWindow amp VPM 324 9 95 Shipping amp handling 13 mail 20 per copy Diskette Q37 O 534 SixGraph Computing Ltd formerly ZUNIQ DATA Corp 2035 C te de Liesse suite 201 Montreal Que Canada H4N 2M5 Tel Tel 514 332 1331 1331 F Fax 514 26 1032 Disaik Smallralk V is a reg iaer PH able Thus multiple inheritance is essential if the system is to have any flexibility at all GARBAGE COLLECTION I m sure you ve all heard this one What if your nuclear power plant has to do a garbage collect in the middle of a meltdown service routine One side argues that garbage collection is thus a bad thing The other says that one would have to be careful in using garbage collection in a hard real time system with stringent response time requirements but that this does not describe most programming WHO S RIGHT Ultimately the more sensible participants will admit there are few if any universally right answers Languages ate designed to meet different goals Criticizing them for not being some thing they were not inte
83. w instance passing the queue han dle as a message parameter The Thread function then loops until a VPM_APPC_STOP_THREAD is received processing mes sages After each message is processed a VPM_APPC_VERB_DONE message is posted to the AppeNotifierWindow instance After the VPM_APPC_STOP_THREAD message is received the Thread func tion stops looping and posts the VPM_APPC_THREAD_STOPPED message which allows us to be absolutely sure the thread has stopped before freeing the stack area A subclass of DynamicLinkLibrary must be created to allow the CreateThread function to be called The AppeDLL class is shown in Listing 2 To communicate with the thread using PM messages there must be a PM window to receive them Since this window will not perform any other functions it should not be visible This may be accomplished by making it a subclass of DDEAuxWindow To facilitate reuse an abstract superclass named InvisibleNoti fierWindow has been created as a subclass of DDEAux Window No tifier windows for various functions are subclasses of this class InvisibleNotifierWindow implements the same when perform in terface as SubPane allowing notifier windows to send messages to their owners when important events occur Listing 3 shows some the of the methods defined for the AppcNotifierWindow As you can see there is a method corresponding to each PM mes sage number defined in PMEventsExtra Companion methods are also defined for each The vpmA
84. ween our MVC components We can see that the only interaction initiated from the model is in the update notification mechanism Other than that there are four meth ods that the view and controller rely on from their model If we had a completely different model but one whose object in terface included the same four selectors as SmallDraw and notified dependents with add we could use the same view and controller with no changes Responsibilities in the application are distributed among the MVC components As such each component has some thing to offer the user by means of the menu The SmallDraw model presents the user with options to change the default inside color border color and line width The SmallDrawView allows the user to change the scale of the displayed objects and the SmallDrawController offers a choice of objects to be drawn Each has its own independent menu but we need a way of combining them into a single menu for presentation on screen and a way to determine who will process the result ing menu selection The operate menu is activated by pressing the operate but ton or by clicking in the menu bar The mallDrawController senses this and asks itself for its menu The SmallDrawController menu method asks its view for its menu If one is returned a new menu is constructed combining the controller s menu and its view s menu In a similar fashion the SmallDrawView menu method asks its model for a menu and answers the
85. wing and for accessing and modifying its other attributes The Smalltalk system classes do not have a ready made graphic view that will do everything that we want so we ll define our own SmallDrawView as a subclass of View The Small DrawView is responsible for displaying the graphic objects of its model an instance of SmallDraw We ll give the SmallDrawView the ability to change the scale of the scene so that we ll be able to zoom in or zoom out It therefore will need to keep track of its current scale and provide some manner of chang ing the scale When the SmallDrawView displays itself it will ob tain the set of objects to be displayed from its model Then the view will ask each object to display itself using the view s The Smalltalk Project Browser Source Code Management System for Smalltalk V The Smalltalk Project Browser from Empower Software allows developers to track and manage changes to the Smalltalk image and enables simplified code sharing and software project organization Designed as a logical extension of the Smalltalk environment this system defines hierarchical projects as collections of classes methods and global variables upon which various operations can be performed Two tools are included The Project Browser is used to define and maintain projects or generate from image changes file projects in and out create object libraries and generate documentation summary encyclopedia of classes
86. y are users don t see them and nobody really has them The notion was that objects are sort of the industry s dirty laundry so they really shouldn t be hung out in decent company We dis agree Objects should not be swept under the rug We know that the notions of object orientation have been around the industry since the early 1970s But we believe that the technology infrastruc ture is only now becoming sufficiently powerful and sophisticated so those notions can be implemented in everyday systems And we think that development will change everything about computing for our readers And we mean everything including what skills you need to be successful what kind of products you should invest in the methods you use to evaluate those products the expectations you have and set for your management about how fast you can imple ment new applications and the approaches you choose to adopt in designing your systems A key benefit of object based systems for instance should be to move the locus of responsibility for applying technology from the vendor to the customer Editorial Object oriented technology needs to be thrashed out Stewart Alsop INFOWORLD 3 2 92 27 WINNED Np PTEE y HWEEK a TEH S AD Cycle LABS ai P35 a3 SHOOT OUT WINDOWS AND OS 2 PROTOTYPE TO DELIVERY NO WAITING In Windows and OS 2 you need prototypes You have to get a sense for what an application is going to look like and

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