C# compiler oddity with delegate constructors

Question

Based on the following question, I found some odd behaviour of the c# compiler.

The following is valid C#:

static void K() {}

static void Main()
{
          


        

Answer 1

The spec (section 7.6.10.5) says:

• The new delegate instance is initialized with the same invocation list as the delegate instance given by E.

Now suppose the compiler translated it to something similar to your suggestion of:

new Action( a.Target, a.Method)

That would only ever create a delegate with an invocation list of a single method call. For a multi-cast delegate, it would violate the spec.

Sample code:

using System;

class Program
{
    static void Main(string[] args)
    {
        Action first = () => Console.WriteLine("First");
        Action second = () => Console.WriteLine("Second");

        Action both = first + second;
        Action wrapped1 =
            (Action) Delegate.CreateDelegate(typeof(Action),
                                             both.Target, both.Method);
        Action wrapped2 = new Action(both);

        Console.WriteLine("Calling wrapped1:");
        wrapped1();

        Console.WriteLine("Calling wrapped2:");
        wrapped2();
    }
}

Output:

Calling wrapped1:
Second
Calling wrapped2:
First
Second

As you can see, the real behaviour of the compiler matches the spec - your suggested behaviour doesn't.

This is partly due to the somewhat odd "sometimes single-cast, sometimes multi-cast" nature of Delegate, of course...