I was looking for a built-in attribute to specify that a type is immutable, and I found only System.ComponentModel.ImmutableObjectAttribute.

Using Reflector, I checked where it was used, and it seems that the only public class that uses it is System.Drawing.Image... WTF? It could have been used on string, int or any of the primitive types, but Image is definitely not immutable, there are plenty of ways to alter its internal state (using a Graphics or the Bitmap.SetPixel method for instance).

So the only class in the BCL that is explicitly declared as immutable, is mutable! Or am I missing something?