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Document number: N3866

Date: 2014-01-19

Invocation type traits (Rev. 2)

by Mike Spertus

Excerpt:

We propose a (compiler-supported) type trait std::invocation_type whose type typedef is the implied function type of the callable object when called with the given argument types.

For example, if we define C as

struct C {
  int operator()(double d, int i);
  int operator()(double d1, double d2);
};

then std::invocation_type<C(int, int)>::type would be int(double, int). More precisely the return type of invocation_type<Fn(ArgTypes...)> is result_of<Fn(ArgTypes...)> and each argument type is the same as the formal parameter type matched in the call to Fn. For more detailed information, see the use cases and wording below.

The main difference between this and previous revisions is that we add two variants of the invocation_type.