Why cannot C# resolve the correct overload in this case?

Question

I've come across a strange situation which is non-ambiguous, yet the overload resolver doesn't think so. Consider:

public static class Program {     delegate int IntDel();     delegate string StringDel();      delegate void ParamIntDel(int x);     delegate void ParamStringDel(string x);      static void Test(IntDel fun) { }     static void Test(StringDel fun) { }     static void ParamTest(ParamIntDel fun) { }     static void ParamTest(ParamStringDel fun) { }      static int X() { return 42; }     static void PX(int x) { }      public static void Main(string[] args)     {         ParamTest(PX); // OK         Test(X); // Ambiguos call!     } } 

How come the call to ParamTest overloads is resolved correctly, but Test overload is ambiguous?

Answer 1

Perhaps because https://msdn.microsoft.com/en-us/library/aa691131%28v=vs.71%29.aspx

The signature of a method specifically does not include the return type, nor does it include the params modifier that may be specified for the right-most parameter.

And the only difference between IntDel and StringDel is in the return value.

More specifically: https://msdn.microsoft.com/en-us/library/ms173171.aspx

In the context of method overloading, the signature of a method does not include the return value. But in the context of delegates, the signature does include the return value. In other words, a method must have the same return type as the delegate.