Why do 2 delegate instances return the same hashcode?

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

c# .net delegates hashcode

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From MSDN :

The default implementation of GetHashCode does not guarantee uniqueness or consistency; therefore, it must not be used as a unique object identifier for hashing purposes. Derived classes must override GetHashCode with an implementation that returns a unique hash code. For best results, the hash code must be based on the value of an instance field or property, instead of a static field or property.

So if you have not overwritten the GetHashCode method, it may return the same. I suspect this is because it generates it from the definition, not the instance.

answered 2011-07-08T12:09:00.633

Why do 2 delegate instances return the same hashcode?

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