What is this Type in .NET (Reflection)

Question

What is this Type in .NET? I am using reflection to get a list of all the classes and this one turns up.

What is it? where does it come from? How is the name DisplayClass1 chosen? I search the sources and didnt see anything. What does the <> mean? what does the c__ mean? is there reference?

enter image description here

I [blogged about this](http://blog.slaks.net/2011/06/delegates-vs-function-pointers-part-4-c.html). — SLaks, Jun 19 '11 at 19:49

score 50 · Accepted Answer · answered Jun 19 '11 at 13:02

50

It's almost certainly a class generated by the compiler due to a lambda expression or anonymous method. For example, consider this code:

using System;

class Test
{
    static void Main()
    {
        int x = 10;
        Func<int, int> foo = y => y + x;
        Console.WriteLine(foo(x));
    }
}

That gets compiled into:

using System;

class Test
{
    static void Main()
    {
        ExtraClass extra = new ExtraClass();
        extra.x = 10;

        Func<int, int> foo = extra.DelegateMethod;
        Console.WriteLine(foo(x));
    }

    private class ExtraClass
    {
        public int x;

        public int DelegateMethod(int y)
        {
            return y + x;
        }
    }
}

... except using <>c_displayClass1 as the name instead of ExtraClass. This is an unspeakable name in that it isn't valid C# - which means the C# compiler knows for sure that it won't appear in your own code and clash with its choice.

The exact manner of compiling anonymous functions is implementation-specific, of course - as is the choice of name for the extra class.

The compiler also generates extra classes for iterator blocks and (in C# 5) async methods and delegates.

answered Jun 19 '11 at 13:02

Jon Skeet

1,421,763
867
9,128
9,194

Excellent explanation. Accepted (when the time comes) – Jun 19 '11 at 13:10
Is there a way to stop this from happening? – Vinnyq12 Sep 17 '12 at 14:08
@Vinnyq12: Beyond "don't use lambda expressions which capture variables other than `this`"? – Jon Skeet Sep 17 '12 at 14:41
@JonSkeet An API requires an Expression as a parameter. When I explicitly set the parameter it is accepted but if I dynamically build up the expression an "ExtraClass" is created and it is no longer accepted :( API is SharePoint. – Vinnyq12 Sep 18 '12 at 14:16
@Vinnyq12: Sounds like you should ask a separate question with lots more detail. – Jon Skeet Sep 18 '12 at 14:30
@JonSkeet I did but no love was given. http://stackoverflow.com/questions/12459073/dynamically-create-params-for-sharepoint-client-object-model-expression-includew – Vinnyq12 Sep 18 '12 at 15:04

score 23 · Answer 2 · edited May 23 '17 at 12:19

Jon is of course correct. I've provided a "decoder ring" for figuring out what the various compiler-generate type names mean here:

Where to learn about VS debugger 'magic names'

The names are quite long and we sometimes get complaints that we're bulking up the size of metadata as a result. We might change the name generation rules to address this concern at any time in the future. It is therefore very important that you not write code that takes advantage of knowledge of this compiler implementation detail.

What is this Type in .NET (Reflection)

2 Answers2

Linked