C# 4.0 introduced several new language features including dynamic typing using the dynamic keyword, optional and named parameters, covariance and contravariance in generics, and improved COM interoperability. The presentation provided an overview of these features and their benefits, demonstrated examples, and discussed how the Dynamic Language Runtime enables dynamic typing in C#.

1. C# 4.0 Language Enhancements Sankarsan Bose 11th October 2009

3. Current Trends

4. C# 4.0 Features

5. Dynamic Objects

6. Named And Optional Parameters

7. Covariance And Contravariance

9. Current Trends C#

11. Optional and Named Parameters

12. Co- and Contra-variance

14. Stores string value

15. “+” operator concatenates

16. Assigned int values

17. “+” operator addsType Determined At Runtime Based On Type Of Value Stored

19. Exactly same signature

20. No type defined for parameter “p”

21. Any object supporting method “print” is a valid input

22. This is called “Duck Typing”Method To Be Invoked Is Decided At Runtime

23. Dynamic Programming Dynamic Method Dispatch in C# (Before 4.0) Both are staticallytyped as IOfficeDocument

25. Statically Typed as “dynamic”

26. Actual type determined at runtimeDynamic Method Invocation

28. Need not implement all methods of interface

31. Dynamic Programming C# is a statically typedlanguage How we are making it dynamic ??? Here Comes DLR Dynamic Language Runtime

33. Caching mechanism for dynamic call

35. Actual method call is delegated to CallSite

36. Compiler Generated Class

38. Optional & Named Parameters “b” & “c” are nullable & optional Calling code has to pass null value This is an issue for large no of parameters

39. Optional & Named Parameters Solution Using Overload in C# (Before 4.0) One overload accepts only “a” Another accepts “a” & “b” This is not possible Signature clash with the previous method

40. Optional & Named Parameters Solution Using C# 4.0 Optional Parameter with Default Value Optional Parameter omitted in the call Method call with parameter names Position reversed

41. Optional & Named Parameters Demo

42. Covariance & Contravariance Subclass Ellipse Circle As per Liskov Substitution Principle(LSP): Any program which expects an object of Ellipse Will function without any change with an object of Circle Covariance – Type substitution as per LSP Contravariance – Type substitution reverse to LSP

43. Covariance & Contravariance Delegate Covariance in C# (Already Present) Func<Base> is a delegate which returns type “Base” Func<Base> can be replaced by function with return type “Derived”

44. Covariance & Contravariance Delegate Contravariance in C# (Already Present) Func<Derived , Object> is a delegate which accepts type “Derived” Func<Base> can be replaced by function which accepts type “Base”

45. Covariance & Contravariance Covariance in Arrays (Existing in C# ) This covariance is allowed This code compiles But throws Runtime Exception

46. Covariance & Contravariance Invariance in Generic Types(Existing in C# ) This covariance is not allowed This code will not compile Before C# 4.0 Generic Types are Invariant

47. Covariance & Contravariance Covariance in Generic Types of C# 4.0 This covariance is allowed public interface IEnumerable<out T> : IEnumerable{IEnumerator<T> GetEnumerator();}

48. Covariance & Contravariance Contravariance in Generic Types of C# 4.0 This Contravariance is allowed public interface IComparer<in T>{ public int Compare(T left, T right);}

49. Covariance & Contravariance Demo

51. Optional and named parameters

52. Dynamic objects

53. No additional type casts needed

55. Improved COM InterOp Take advantage of named parameters & optional arguments

56. Improved COM InterOp Take advantage of named parameters & optional arguments

57. Improved COM InterOp Demo

58. Journey of C# - Revisited Dynamic Functional + LINQ Generics Static Language + Managed Code

59. Thank You

61. http://channel9.msdn.com/posts/Charles/C-40-Meet-the-Design-Team/

62. http://channel9.msdn.com/shows/Going+Deep/Expert-to-Expert-Anders-Hejlsberg-The-Future-of-C/

63. http://channel9.msdn.com/pdc2008/TL16/