Lambda Expressions and Expression Trees

MSDN Blog Postings » Lambda Expressions and Expression Trees

MSDN Blog Postings » Lambda Expressions and Expression Trees — Wed, 12 Sep 2007 07:45:59 GMT

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re: Lambda Expressions and Expression Trees

Fduch — Sat, 15 Sep 2007 03:00:26 GMT

Please!

Fix the bug with VB lambda expressions in Beta 2.

These same line of code comile to very different IL and return different results in VB and C#.

I don't understab why, but VB compiler generates closures for this code and returns wrong results.

delegate TReturn SelfApplicable0<TReturn>(SelfApplicable0<TReturn> self);

SelfApplicable0<Func<Func<Func<int, int>, Func<int, int>>, Func<int, int>>> YC = y => f => x => f(y(y)(f))(x);

Delegate Function SelfApplicable0(Of TReturn)(ByVal self As SelfApplicable0(Of TReturn)) As TReturn

Dim YC As SelfApplicable0(Of Func(Of Func(Of Func(Of Integer, Integer), Func(Of Integer, Integer)), Func(Of Integer, Integer))) = Function(y) Function(f) Function(x) f(y(y)(f))(x)

re: Lambda Expressions and Expression Trees

VBTeam — Wed, 19 Sep 2007 20:56:06 GMT

Hi there,

Thanks for posting this suggestion. The behavior is actually by design, and not a bug at all. If you run the code you'll notice the output is exactly the same as C#.

VB's closures are the same as C#'s display classes. In the C# example, there is a nesting level of 2 display classes. In VB, we have a nesting level of 3 closures. C# chose to optimize one level of display classes away by creating a static function for lambdas that don't lift variables. VB chose not to do this optimization because these classes would then not be hostable in the SQL CLR.

Hope that helps,

Jonathan Aneja

PM, VB Team

VB 2008 Language Deep Dive - Presentation Materials (Jonathan Aneja)

The Visual Basic Team — Thu, 21 Aug 2008 08:09:25 GMT

Last week I got the chance to visit the Toronto .NET User Group and give a talk on all the great new