c# - Can’t assign to delegate an anonymous method with less specific parameter type

Question

I’m able to assign a method M to delegate object d with a less specific parameter type, but when I want to assign an anonymous method with same the signature as method M to d, I get an error.

Why is that?

class derivedEventArgs : EventArgs { }

delegate void newDelegate(object o, derivedEventArgs e); 

static void Main(string[] args)
{
    newDelegate d = M; // ok
                d = (object o, EventArgs e) => { }; // error
}

public static void M(object o, EventArgs e) { }

Answer 1

This is covered in section 6.5 of the C# language specification. If you explicitly type the parameters of an anonymous function, they must match in both type and modifiers in order to be compatible signatures.

Specifically, a delegate type D is compatible with an anonymous function F provided

...

If F has an explicitly typed parameter list, each parameter in D has the same type and modifiers as the corresponding parameter in F.