For Dummies C# 2010 All-in-One
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1. Line six will not compile even if the Schedule method exists because we can t assume that newCourse will always come back as a Course object because it is declared a variant We are stuck With a dynamic type though we are golden once again with this code CourseMarshaller cm new CourseMarshaller a COM object int courseld 4 dynamic newCourse cm MakeCourse courselId newCourse newCourse Schedule This now compiles Book VIII Chapter 1 jAjjeotweukg Hurwwesboig 114 Putting Dynamic to Use What happens if newCourse comes back as something that doesn t have a Schedule method You get a runtime error But there are try catch blocks for runtime errors Nothing will help it compile without the dynamic keyword Readers who are long time Visual Basic programmers or even newer VB NET programmers realize that you can handle this dynamically and have always been able to in Visual Basic For a long time I have recommended that programmers working with legacy systems use Visual Basic for their new code and this is exactly why In the interest of language parity now C can do it too In general this is good because many organizations are writing legacy code in VB and new code in C and it can get pretty messy in the trenches This change makes the code base slimmer Putting Dynamic to Use When C encounters a dynamic typed variable like the variables we created earlier it changes everythin2. able The compiler will just figure it out for you In a static language like C 3 0 you do have to say what type you are making that variable Microsoft originally promised that dynamic types would never be in C but later decided that the feature had to be added Why Mostly it s because of the development for Microsoft Office like the reasoning for much of the rest of Book VIII Office uses COM the pre NET structure for Microsoft applications 770 Shifting C Toward Dynamic Typing COM expects that the languages that use it like VB Classic and C will have dynamic types This made developing for Microsoft Office difficult for C programmers which was exactly opposite of what Microsoft wanted to happen The end result The dynamic type Shifting C Toward Dynamic Typing So called dynamic languages are a trend that keeps coming back like ruf fled tux shirts Dynamic languages are languages that allow for loose typing rather than static The concept got started in the 1960s with LISP Dynamic languages came back in the late 1980s for two reasons network management scripting and the artificial intelligence craze Thanks to the Web the buzz word is back yet again The World Wide Web for those of you who aren t old enough to remem ber was built on View Source and dynamic languages Microsoft s original Web development language Active Server Pages was built on VBScript a dynamic language The Web is bett
3. IronPython c Visual Basic Microsoft NET Binder Dynamic Language Runtime w Binder ay Expression Call Site Dynamic Object Silverlight Trees Caching Interoperability Binder i J pr Common Language Runtime CLR Office The runtime helps the compiler to construct code in the compiled assembly that will make a lot of choices dynamically The code block at the end of the preceding section is an example of the simplest kind The DLR assisted in the creation of IRONRuby which makes it possible to code in Ruby the current hot dynamic language right in Visual Studio Of course because the DLR enables C to take on dynamic language fea tures much that you can do in Ruby you can now do in C Dynamic Ruby Ruby takes advantage of its dynamic roots in its implementation of the Trabb Pardo Knuth algorithm Don t be put off by the name this is just a straightforward problem that can be solved by computer code The program needs to read 11 numbers from an input device in our case the console s ReadLine method It stores them in an array Then it pro cesses the array backward starting from the last entered value with some function If the value doesn t exceed some arbitrary threshold it prints the result The program looks like this in Ruby class TPK def f x return Math sqrt x abs 5 x 3 end Book VIII Chapter 1 jAjjeotweudg Hurwwesboig 1 8 Running with the Dynamic Language Runtim
4. macros in previous versions of Visual Studio you know what a pain it is to use a static language Making C and VB NET for that matter more dynamic not only makes it a better language for extending Visual Studio but it also gives programmers the capability to include the language in the programs they write so that other developers can further extend those applications Programming Dynamically By now you must be asking What exactly are we talking about here Fair question When you define a new variable you can use the dynamic keyword and C will let you make assumptions about the members of the variable More or less what I m talking about it this If you want to declare a new Course object you do it like this Course newCourse new Course newCourse Schedule This is of course assuming that you have a Course class defined somewhere else in your program like this class Course public void Schedule Something fancy here But what if you don t know what class the new object will be How do you handle that You could declare it as an Object because everything derives from Object right Here s the code Object newCourse new Object Not so fast my friend if you make your next line this newCourse Schedule Note the squiggly line appears almost immediately and you get the famous object does not contain a definition for Schedule error in the design time Error Lis
5. MBER KV amp Chapter 1 Programming Dynamically In This Chapter Understanding dynamic typing Defining variables Putting dynamic to use Making static operations dynamic Fe many years I thought that dynamic programming referred to being really flashy and flamboyant while writing code So I started wearing Hawaiian shirts and singing loudly Later I found out this isn t the case Dynamic programming is another one of those buzzwords that really doesn t have a clear definition At its loosest it means developing something in such a way that the program makes more decisions about the way it runs while running rather than when you compile it Scripting languages are a great example of this When you write something in VBScript you don t compile it at all all of the decisions are made at runtime Ruby is another good example Most of the time an entire program can just be typed into a command prompt and run right from there There are examples that are not so good like VB Classic Remember the Variant type You could declare a variable to be Variant and VB wouldn t decide what it was supposed to be for real until the program ran In the best of cases this added immense flexibility to the language In the worst of cases you got Type Mismatch errors at runtime To give a concrete example when you declare a variable in a dynamically typed language you don t have to say what type you are making that vari
6. asks for two reasons First they provide instant feedback because you can try a piece of code outside the constraints of the rest of the program you are writing Second you can start building your higher level pieces of code without building the plumbing that makes it work For instance Ruby has a command line interface that you can simply paste a function into even out of context and see how it works There is even a Web version at http tryruby hobix com You can type code right in there even if there are classes referenced that aren t defined because Ruby will just take a guess at it This moves nicely into the next point that a dynamic language enables you to build a class that refers to a type that you haven t defined elsewhere For example you can make a class to schedule an event without actually having to build the underlying Event type first All of this lends itself to a language that is a lot more responsive to change You can make a logic change in one place and not have to dig through reams of code to fix all the type declarations everywhere Add this to optional and named parameters see Chapter 2 and you have a lot less typing to do when you have to change your program Book VIII Chapter 1 jAjjeotweukg Hurwwesboig 112 Programming Dynamically Other benefits to dynamic languages in general show up as you use them more For instance macro languages are usually dynamically typed If you have tried to build
7. at error much easier and handle it right on user input Book VIII Chapter 1 jAjjeotmeudg Hurwwesboig 780 Running with the Dynamic Language Runtime Add to that the reality that C is making runtime decisions about every single variable throughout the entire run of the program That s a whole lot of extra processing that we could have avoided if we had just done that static typing The take home here is that using dynamic types makes your programming job much easier and your troubleshooting job much harder If you are writ ing a utility script for your own use and don t care if it occasionally crashes with a type mismatch then use dynamic If you are writing a backup script for a hospital and the lives of thousands are at stake I advise static types
8. e def main Array new 11 gets to_i reverse each do x y x puts x y gt 400 TOO LARGE y end end end This isn t a Ruby book and that fact isn t lost on me Nonetheless this is the best dynamic language that I can use for an example bar none Two functions are defined and main Main accepts 11 numbers from the console and then moves them to an integer array that s what gets to_i does For each value in the array it sets y equal to f x and then sees if it is higher than our arbitrary value If so it prints TOO LARGE otherwise it prints the number Why is being dynamic important for this algorithm It isn t You could do it all statically typed The dynamic bit does have an impact though First x doesn t care what x is The program assumes that whatever comes in gets changed to an integer at gets to_i but the function itself is case agnostic This is good and bad because if we do happen to give it a string or some other type it will fail The array itself isn t typed either This can have benefits because it is pos sible to drop a differently typed value in there if you know you are just going to write it to the screen Dynamic C Of course C now has similar features right We should be able to do the same thing Yes in fact we can Here s the code static dynamic f dynamic x i return Math Sqrt x 5 0 Math Pow x 3 0 AER void Main string ar
9. e compiler chooses to make a static operation dynamic as it did in item 6 in the preceding section the compiler rebuilds the code on the fly to have it handle the dynamic variable What does that mean for you Glad you asked Let s take item 6 Console WriteLine dynamicVariable This piece of code forces the compiler to build intermediary code which checks for the type of variable at runtime in order to come up with something that is writ able to the console The compiled code first checks if the input is a static type that it knows Next it checks for a type present in the program Then it will just try a few things that might work It will fail with an error if it finds nothing If this must happen that s fine But remember that it is slower than all git out This is why Variant got such a bad rap in Visual Basic classic Dynamic is something you don t use until you need it It puts a tremendous strain on the machine running the program especially if all variables are dynamic Understanding what s happening under the covers Let s take an example right out of MSDN Microsoft points out this simple method class C public dynamic MyMethod dynamic d return d Foo This is pretty straightforward stuff a method that accepts a dynamic class and returns the results of the type s Foo method Not a big deal Book VIII Chapter 1 jAjjeotweudg Hurwwesboig 776 Running with the Dynamic Language Ru
10. er with a dynamic programming environment so the trend is probably here to stay this time until the next big thing anyway C isn t the only language that is adding dynamic language features and dynamic type isn t the only language feature that has been added to make it more appealing for Web programmers Several dynamic languages have been around for a while like these Perl Visual Basic Smalltalk LISP Scheme While some of these aren t as popular as they once were they are still out there and have pushed the trend in the newer languages You can see this trend in all the new or refurbished dynamic languages that have popped up over the last ten years Many of them have roots in the Web while others are being newly used for the Web PHP Ruby JavaScript Cold Fusion Shifting C Toward Dynamic Typing 771 Python Cobra my new favorite Groovy Boo Newspeak Programmers who work in dynamic languages how can I put this gently feel strongly about their choice of tools The communities are very strong Developers who work in dynamic languages use them for practically every thing except highly structured team build kinds of environments like Scripting infrastructure for system maintenance Building tests One use utilities Server farm maintenance Scripting other applications Building Web sites File maintenance 4 4 Dynamic languages are popular for these kinds of t
11. g that variable touches into a dynamic operation This dynamic conversion means that when you use a dynamically typed object in an expression the entire operation is dynamic Classic examples There are six examples of how this works Say we have the dynamic vari able dynaVariable Because the dynamic variable will pass through all six examples they will all be dispatched dynamically by the C compiler Here are those examples with nods to Daniel Ng dynamicVariable someMethod a b c The compiler binds the method someMethod at runtime since dynaVariable is dynamic No surprise dynamicVariable someProperty 42 The compiler binds the property someProperty just like it did in the first method var newVar dynamicVariable 42 The compiler looks for any overloaded operators of with a type of dynamic Lacking that it out puts a dynamic type int newNumber dynamicVariable This is an implicit conversion to int The runtime determines if a conversion to int is possible If not it throws a type mismatch error Putting Dynamic to Use 175 int newString int dynamicVariable This is an explicit cast to int The compiler encodes this as a cast you actually change the type here Console WriteLine dynamicVariable Because there is no over load of WriteLine that accepts a dynamic type explicitly the entire method call is dispatched dynamically Making static operations dynamic If th
12. gs i dynamic array new Array 11 for int i 0 i lt 11 i l array i Console ReadLine ie int i 10 i gt 0 i Figure 1 2 The TPK program running Running with the Dynamic Language Runtime 779 dynamic y f array il if y gt 400 0 Console WriteLine string Format 0 TOO LARGE i jelse Console WriteLine 0 1 i array 1 Console ReadKey Line for line the application does the same thing as the Ruby code albeit longer I kept the names the same so it was easier to follow Because I had to use for loops to handle the integrators it made the body of the program quite a bit beefier Figure 1 2 shows what the program looks like when it runs ers Bill Documents Visual Studio 2010 Projects TPK TPKIbin Debug TPK EXE loo jeas But why use the dynamic type here Clearly we could have just used double for this Use of dynamic just made the program easier to create Try chang ing the array to an array of double like this Double array new Double 11 Hey look at that Now the ReadLine doesn t work We ll just cast it to a double Nope can t do that we have to use TryParse You get the picture Static types are hard to code with Dynamic types are easier to code with What s the other side of this Well obviously if the user enters a string she gets a runtime error and that is bad If we statically type everything then we can trap th
13. ntime Here is the compiled C code class C return Dynamic public object MyMethod Dynamic object d if MyMethodo__SiteContainer0 p__Sitel null MyMethodo__SiteContainer0O p__Sitel CallSite lt Func lt CallSite object object gt gt Create new CSharpCallPayload CSharpCallFlags None Foo typeof object null new CSharpArgumentiInfo new CSharpArgument Info CSharpArgumentInfoFl ags None null return MyMethodo__SiteContainer0 p__Sitel Target MyMethodo__SiteContainer0 p__Sitel d CompilerGenerated private static class MyMethodo__SiteContainer0 public static CallSite lt Func lt CallSite object object gt gt p_ Sitel J Yeah that s what I said too I am not going to even begin to try breaking down this code and fortunately we don t have to That s what we have compilers for right Running with the Dynamic Language Runtime There is more to dynamic languages than just the dynamic typing You can do some powerful things Like all power you have to be careful not to misuse it The Dynamic Language Runtime shown in Figure 1 1 is a library added to the NET Framework specifically to provide for adding dynamic languages like Ruby to the Visual Studio fold like IRONRuby or to add dynamic lan guage features to existing static languages like C 4 0 Figure 1 1 The Dynamic Language Runtime Running with the Dynamic Language Runtime 177 IronRuby
14. t Programming Dynamically 173 However we can do this dynamic newCourse SomeFunction newCourse Schedule All this code needs to have is the stub of a function that returns some value and we are good to go What if SomeFunction returns a string Well we will get a runtime error But it will still compile About now if you are anything like me you have to be thinking This is a good thing How I hear you trust me For the time being you can blame COM You see COM was mostly constructed using C which has a variant type In C you could declare a variable to be dynamic like this VARIANT newCourse It worked just like the dynamic type except C wasn t invented yet Anyway because a lot of the objects in COM used Variant out parameters it was really tough to handle Interop using NET Because Microsoft Office is mostly made of COM objects and because it isn t going to change any time soon and because Microsoft wants us all to be Office developers one day bam we have the dynamic type Say for instance that our newCourse is a variant out parameter from a method in a COM class In order to get the value we have to declare it an Object like this CourseMarshaller cm new CourseMarshaller a COM object int courseld 4 Object newCourse cm MakeCourse courselId newCourse and now we are back to square one newCourse Schedule This causes a member not found exception
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