Defined in header <concepts> | ||
---|---|---|
template< class F, class... Args > concept invocable = requires(F&& f, Args&&... args) { std::invoke(std::forward<F>(f), std::forward<Args>(args)...); /* not required to be equality preserving */ }; | (since C++20) | |
template< class F, class... Args > concept regular_invocable = std::invocable<F, Args...>; | (since C++20) |
The invocable
concept specifies that a callable type F
can be called with a set of argument Args...
using the function template std::invoke
.
The regular_invocable
concept adds to the invocable
concept by requiring the invoke
expression to be equality preserving and not modify either the function object or the arguments.
An expression is equality preserving if it results in equal outputs given equal inputs.
In specification of standard concepts, operands are defined as the largest subexpressions that include only:
std::move
, std::forward
, and std::declval
. The cv-qualification and value category of each operand is determined by assuming that each template type parameter denotes a cv-unqualified complete non-array object type.
Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.
Unless noted otherwise, every expression used in a requires-expression is required to be equality preserving and stable, and the evaluation of the expression may modify only its non-constant operands. Operands that are constant must not be modified.
The distinction between invocable
and regular_invocable
is purely semantic.
A random number generator may satisfy invocable
but cannot satisfy regular_invocable
(comical ones excluded).
(C++17) | checks if a type can be invoked (as if by std::invoke ) with the given argument types (class template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/concepts/invocable