C# Language Specification

Finding the best common type of a set of expressions

In some cases, a common type needs to be inferred for a set of expressions. In particular, the element types of implicitly typed arrays and the return types of anonymous functions with block bodies are found in this way.

Intuitively, given a set of expressions E₁…E_m this inference should be equivalent to calling a method

T_r M(X x₁ … X x_m)

with the E_i as arguments.

More precisely, the inference starts out with an unfixed type variable X. Output type inferences are then made from each E_i to X. Finally, X is fixed and, if successful, the resulting type S is the resulting best common type for the expressions. If no such S exists, the expressions have no best common type.

3.