std::invocable, std::regular_invocable
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 arguments 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.
Equality preservation
Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).
Notes
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).
References
- C++23 standard (ISO/IEC 14882:2024):
- 18.7.2 Concept
invocable[concept.invocable] - 18.7.3 Concept
regular_invocable[concept.regularinvocable] - C++20 standard (ISO/IEC 14882:2020):
- 18.7.2 Concept
invocable[concept.invocable] - 18.7.3 Concept
regular_invocable[concept.regularinvocable]
See also
|
(C++17)(C++17)(C++17)(C++17) | checks if a type can be invoked (as if by std::invoke) with the given argument types (class template) |
External links
A joke example of a random number generator that satisfies both invocable and regular_invocable. |
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https://en.cppreference.com/cpp/concepts/invocable
