My morbid curiosity has me wondering why the following fails:
// declared somewhere
public delegate int BinaryOperation(int a, int b);
// ... in a method body
Func<int, int, int> addThem = (x, y) => x + y;
BinaryOperation b1 = addThem; // doesn't compile, and casting doesn't compile
BinaryOperation b2 = (x, y) => x + y; // compiles!
C# has very limited support for "structural" typing. In particular, you can't cast from one delegate-type to another simply because their declarations are similar.
From the language specification:
Try one of:
Here's a similar question: why doesn't this compile?
In this case it seems a little more natural for the cast to not work, but it's really the same reason.