std::result_of, std::invoke_result

Since C++17

Header: <type_traits>

Deduces the return type of an INVOKE expression at compile time.

# Declarations

template< class >
class result_of; // not defined
template< class F, class... ArgTypes >
class result_of<F(ArgTypes...)>;

(since C++11) (deprecated in C++17) (removed in C++20)

template< class F, class... ArgTypes >
class invoke_result;

(since C++17)

# Notes

As formulated in C++11, the behavior of std::result_of is undefined when INVOKE(std::declval(), std::declval()…) is ill-formed (e.g. when F is not a callable type at all). C++14 changes that to a SFINAE (when F is not callable, std::result_of<F(ArgTypes…)> simply doesn’t have the type member).

The motivation behind std::result_of is to determine the result of invoking a Callable, in particular if that result type is different for different sets of arguments.

F(Args…) is a function type with Args… being the argument types and F being the return type. As such, std::result_of suffers from several quirks that led to its deprecation in favor of std::invoke_result in C++17:

To avoid these quirks, result_of is often used with reference types as F and Args…. For example:

# See also