C# 4.0

1. Dynamic internals C# 4.0

2. Introductions • Alexandru Ghiondea • C# Compiler QA • ghiondea.alexandru@microsoft.com • http://blogs.msdn.com/alexghi • What is your programming language of choice? • Do your apps interop with COM? Do you use dynamic languages? • Have you seen C# 4.0 before?

3. C# 4.0 language features • Named and Optional parameters • Omit “ref” for COM calls • noPIA • Co&Contra Variance • Dynamic

4. Why dynamic? • There is a lot of interest in accessing the highly dynamic object model of HTML DOM • COM is heavily used and the interop code could be easier to read and write • Dynamic languages are becoming increasingly popular • We need a unified way to work with all of the above

5. Architecture IronPython IronRuby C# VB.NET Others… Dynamic Language Runtime Expression Trees Dynamic Dispatch Call Site Caching ObjectBinder JavaScriptBinder PythonBinder RubyBinder COMBinder

6. How dynamic works • We have a new type called dynamic • Calls on variables of type dynamic are treated differently by the compiler • We package extra information about the call • Calls can be: Method calls, property access, indexer call, operator call • There is a C# runtime binder to interpret the information (at runtime) • It uses the runtime type for all dynamic arguments • It uses the compile time type for all other arguments

7. How dynamic works (2) CLR Expression Tree COM Binder Exe IronPython Binder Bind call Compile Run Dynamic Call Delegate DLR C# Runtime Binder Cache …

8. IronPython, PowerPoint and C# Demo

9. Under the cover • What is the Dynamic type? • There is no dynamic type . There is only object! • What operations are supported? • A variable of type dynamic is assumed to support any kind of operation (method call, property access, operator call and indexer call) • How is the information about the call stored? • Using CallSites objects the compiler packages data about the call

10. What does a CallSite contain? • Information about the call being made • What type of call (method call, property, operator, etc) • The name of the member • The context of the call • The type arguments for the call • Information about the parameters and return types • Is it a constant, is it passed by-ref, etc

11. Dynamic and CallSites Demo

12. Dynamic FAQ • When do you go dynamic? • When the target of the call or any of it’s parameters are dynamic • What is the return type of a dynamic call? • It is dynamic in most cases* • *What about conversions and constructors? • They are dispatched at runtime, but their return type is known at compile time

13. Dynamic FAQ (2) • What about private methods? • Information about the context of call is embedded in the CallSite allowing the Binder to “do the right thing” • Calling a method off a non-dynamic target with dynamic arguments. (c.M(d)); • It works as expected! • Can dynamic “cross” assembly boundaries? • Yes, we decorate any dynamic parameter or return type with a DynamicAttribute • It works for generic types constructed with dynamic as well 

14. Dynamic FAQ (3) • Can I use Named and Optional with dynamic? • Yes! • And also Co & Contra variance • Where can’t I use dynamic? • Lambda expressions • LINQ • Can’t use dynamic and method groups • throw or catch statements

15. Return type, private methods and generics Demo

16. Build you own dynamic object • It’s simple! • Implement IDynamicObject • Derive from DynamicObject • Implements IDynamicObject

17. I want to be dynamic!!! Demo

18. Additional Resources • C# 4.0 Samples and Whitepaper • http://code.msdn.microsoft.com/csharpfuture • Visual C# Developer Center • http://csharp.net • C# team member’s blogs on dynamic • http://blogs.msdn.com/cburrows/ • http://blogs.msdn.com/samng/ • http://blogs.msdn.com/sreekarc/ • http://blogs.msdn.com/alexghi/