This document discusses new features in C# 4.0 and .NET 4.0 including optional and named parameters, covariance and contravariance, dynamic binding, threading using tasks, the task parallel library (TPL), and PLINQ. It includes sample code and questions to test understanding.

1. C# 4.0 and .NET 4.0Buu Nguyen, MVP (ASP.NET)www.buunguyen.net/blogbuunguyen@kms-technology.comMicrosoft Confidential1

2. AgendaOptional and Named ParametersCovariance and ContravarianceDynamic BindingThreading with Task APITask Parallel Library (TPL)PLINQ

3. Optional and Named Parameters

4. ?QuizWhat are 2 issues of this API?

5. Covariance and Contravariance

6. ?QuizWhat is wrong with this code?

7. Covariance DefinedLet’s say S is subtype of B and GT is a generic typeGT<S> behaves like subtype of GT<B> on assignment compatibility, i.e.GT<S> s = …GT<B> b = s;GT<S> s = (GT<S>)b;Safe only when GT doesn’t expose members “receiving” T as input (aka input-safe)Microsoft Confidential7

8. ?QuizWhat is wrong with this code?

9. Contravariance DefinedLet’s say S is subtype of B and GT is a generic typeGT<B> behaves like subtype of GT<S> on assignment compatibility, i.e.GT<B> b = …GT<S> s = b;GT<B> b = (GT<B>)s;Safe only when GT doesn’t expose members “returning” T as output (aka output-safe)Microsoft Confidential9

10. Dynamic Binding

11. ?QuizWrite a method that prints out the Name property of an anonymous object returned by another method

12. Dynamic binding means…use runtime type for all bindings

13. ?QuizA method summing Length properties of all parameters, regardless of actual type

14. ?QuizHow to builds C# objects that behave like JavaScript objects, i.e. members can be added at any time?

15. ?QuizWrite a class whose objects can invoke static methods of any particular typeBonus #1: include non-public static methodsBonus #2: ignore case

16. ?QuizWrite a class whose objects can be used as result-caching proxy for the method invocation of any other object

17. Task Parallel Library (TPL) & PLINQ

18. ?QuizWrite a method calculating Fibonacci number using a thread in thread-pool and returning result to caller

19. Task Parallelism FeaturesWait on tasksSupport parent-child relationshipException handlingCancelling tasksContinuationExecute one task after anotherMicrosoft Confidential19

20. ?QuizWrite 3 methods:Calculate some known Fibonacci numbersCalculate Fibonacci numbers for a rangeCalculate Fibonacci numbers for a list of specified indexesEach calculation must take place in a thread in thread-pool

21. Parallel ClassAssign delegates to a handful of Task instances, not one-to-one mapping

22. ?QuizWrite a method which calculate some specified Fibonacci numbers and return the sum of them to the caller