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Document number: N3729

Date: 2013-09-02

Invocation type traits

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.