C# Language Specification

Delegate compatibility

A method or delegate M is compatible with a delegate type D if all of the following are true:

• 
  D and M have the same number of parameters, and each parameter in D has the same ref or out modifiers as the corresponding parameter in M.
  
• 
  For each value parameter (a parameter with no ref or out modifier), an identity conversion (§6.1.1) or implicit reference conversion (§6.1.6) exists from the parameter type in D to the corresponding parameter type in M.
  
• 
  For each ref or out parameter, the parameter type in D is the same as the parameter type in M.
  
• 
  An identity or implicit reference conversion exists from the return type of M to the return type of D.
  

3.