C# 3.0 generic type inference - passing a delegate as a function parameter

Question

I am wondering why the C# 3.0 compiler is unable to infer the type of a method when it is passed as a parameter to a generic function when it can implicitly create a delegat

Answer 1

That is slightly odd, yes. The C# 3.0 spec for type inference is hard to read and has mistakes in it, but it looks like it should work. In the first phase (section 7.4.2.1) I believe there's a mistake - it shouldn't mention method groups in the first bullet (as they're not covered by explicit parameter type inference (7.4.2.7) - which means it should use output type inference (7.4.2.6). That looks like it should work - but obviously it doesn't :(

I know that MS is looking to improve the spec for type inference, so it might become a little clearer. I also know that regardless of the difficulty of reading it, there are restrictions on method groups and type inference - restrictions which could be special-cased when the method group is only actually a single method, admittedly.

Eric Lippert has a blog entry on return type inference not working with method groups which is similar to this case - but here we're not interested in the return type, only on the parameter type. It's possible that other posts in his type inference series may help though.