Question

Take the following:

  var x =  new Action(() => { Console.Write("") ; });
  var y = new Action(() => { });
  var a = x.GetHashCode();
  var b = y.GetHashCode();
  Console.WriteLine(a == b);
  Console.WriteLine(x == y);

This will print:

True
False

Why is the hashcode the same?

It is kinda surprising, and will make using delegates in a Dictionary as slow as a List (aka O(n) for lookups).

Update:

The question is why. IOW who made such a (silly) decision?

A better hashcode implementation would have been:

return Method ^ Target == null ? 0 : Target.GetHashcode();
// where Method is IntPtr

Answer 1

Easy! Since here is the implementation of the GetHashCode (sitting on the base class Delegate):

public override int GetHashCode()
{
    return base.GetType().GetHashCode();
}

(sitting on the base class MulticastDelegate which will call above):

public sealed override int GetHashCode()
{
    if (this.IsUnmanagedFunctionPtr())
    {
        return ValueType.GetHashCodeOfPtr(base._methodPtr);
    }
    object[] objArray = this._invocationList as object[];
    if (objArray == null)
    {
        return base.GetHashCode();
    }
    int num = 0;
    for (int i = 0; i < ((int) this._invocationCount); i++)
    {
        num = (num * 0x21) + objArray[i].GetHashCode();
    }
    return num;
}

Using tools such as Reflector, we can see the code and it seems like the default implementation is as strange as we see above.

The type value here will be Action. Hence the result above is correct.

UPDATE