C# Language Specification

Type inference for conversion of method groups

Similar to calls of generic methods, type inference must also be applied when a method group M containing a generic method is converted to a given delegate type D (§6.6). Given a method

T_r M1…X_n>(T₁ x₁ … T_m x_m)

and the method group M being assigned to the delegate type D the task of type inference is to find type arguments S₁…S_n so that the expression:

M1…S_n>

becomes compatible (§15.1) with D.

Unlike the type inference algorithm for generic method calls, in this case there are only argument types, no argument expressions. In particular, there are no anonymous functions and hence no need for multiple phases of inference.

Instead, all X_i are considered unfixed, and a lower-bound inference is made from each argument type U_j of D to the corresponding parameter type T_j of M. If for any of the X_i no bounds were found, type inference fails. Otherwise, all X_i are fixed to corresponding S_i, which are the result of type inference.

14.