Features added in .net 4.0 [closed]

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Can you give me the features added in .net 4.0 version and how does it differentiate with .net 3.5 version? Describe?

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What's New in the .NET Framework 4
http://msdn.microsoft.com/en-us/library/ms171868.aspx

27 New Features of .NET Framework 4.0
http://msdotnetsupport.blogspot.com/2009/06/27-new-features-of-net-framework-40.html

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As your question is tagged C# I assume you just want to know those features added to the language:

Dynamic lookup

Dynamic lookup allows you to write method, operator and indexer calls, property and field accesses, and even object invocations which bypass the C# static type checking and instead gets resolved at runtime.

Named and optional parameters

Parameters in C# can now be specified as optional by providing a default value for them in a member declaration. When the member is invoked, optional arguments can be omitted. Furthermore, any argument can be passed by parameter name instead of position.

COM specific interop features

Dynamic lookup as well as named and optional parameters both help making programming against COM less painful than today. On top of that, however, we are adding a number of other small features that further improve the interop experience.

Variance

It used to be that an IEnumerable wasn’t an IEnumerable. Now it is – C# embraces type safe “co-and contravariance” and common BCL types are updated to take advantage of that.

From http://blogs.lessthandot.com/index.php/DesktopDev/MSTech/the-new-features-in-c-4

The source document is here: New features in C# 4.0