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Posted 10 Nov 2011

Delegates internals

, 10 Nov 2011
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I have found a few interesting things which I would like to share with you all.

I was just digging inside the delegates, action and anonymous delegates via lambda expression. I started to ask a few curious questions to myself and thus set out to dig inside to answer them. While doing so, I found a few interesting things which I would like to share with you all. Hope it is useful:

First I wrote a sample code as shown below:

Action del = () => Console.WriteLine("Hello");

Well yes, the code is very simple, but I started to wonder and asked a question myself, what is the difference between the above two different styles of delegate invocation.

If in case you’re not aware of it, every delegate internally is represented as a class type having just four important methods: BeginInvoke, Invoke, EndInvoke, and Ctor. There is nothing much to explain about these methods.

I looked inside the IL and came to know that the above two styles of delegate invocation is in fact the same. The compiler just converts del() to del.Invoke(). So there will be two del.Invoke() statements as shown in the below IL opcodes:

IL_0022: callvirt instance void [mscorlib]System.Action::Invoke()
IL_0027: nop
IL_0028: ldloc.0
IL_0029: callvirt instance void [mscorlib]System.Action::Invoke()

Next I asked myself how lambda expressions used above are treated internally. I found out that the lambda expression which I was using in the code is treated as a class internally in the IL. The below code produced two classes for the anonymous delegates I used:

MyDelegate del = () => (2 + 2).ToString();
del = () => (4 + 4).ToString();\

Let's look into the IL and see what charm the compiler has done:

// Fields
.field private static class ConsoleApplication.Program/MyDelegate ‘CS$<>9__CachedAnonymousMethodDelegate2′
.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
01 00 00 00
.field private static class ConsoleApplication.Program/MyDelegate ‘CS$<>9__CachedAnonymousMethodDelegate3′
.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
01 00 00 00

As you can see, it has produced two classes for each of those anonymous delegates with the name shown above. No matter where the anonymous delegates are declared, they do get the same naming styles. But I still wonder and look for an answer why all anonymous delegates are prefixed with CS$<>9__. May be Microsoft chose to keep it that way? No idea! If you know, kindly leave a comment.

That’s all I could find so far, I shall surely share more if I find out more :)


P.S: Your comment/vote are much appreciated :)


This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)


About the Author

Software Developer (Senior) Siemens
India India
A .net developer since 4+ years, wild, curious and adventurous nerd.

Loves Trekking/Hiking, animals and nature.

A FOSS/Linux maniac by default Wink | ;)

An MVP aspirant and loves blogging ->

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