Callable
C++ concepts: Callable
A Callable type is a type for which the INVOKE operation (used by, e.g., std::function, std::bind, and std::thread::thread) is applicable. This operation may be performed explicitly using the library function std::invoke. (since C++17).
Requirements
The type T satisfies Callable if.
Given.
f, an object oftypeT
The following expressions must be valid:
| Expression | Requirements |
|---|---|
| INVOKE<R>(f, std::declval<ArgTypes>()...) | the expression is well-formed in unevaluated context |
where INVOKE<R>(f, t1, t2, ..., tN) is defined as static_cast<void>(INVOKE(f, t1, t2, ..., tN)) if R is possibly cv-qualified void, otherwise (since C++17) INVOKE(f, t1, t2, ..., tN), implicitly converted to R.
where INVOKE(f, t1, t2, ..., tN) is defined as follows:
- i
ffis a pointer to memberfunction ofclassT:
Notes
For pointers to member functions and pointers to data members, t1 may be a regular pointer or an object of class type that overloads operator*, such as std::unique_ptr or std::shared_ptr.
Pointers to data members are Callable, even though no function calls take place.
Standard library
In addition, the following standard library facilities accept any Callable type (not just FunctionObject).
| std::function |
|:----|
| std::bind |
| std::result_of |
| std::thread::thread |
| std::call_once |
| std::async |
| std::packaged_task |
| std::reference_wrapper |
See also
| is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17) | checks if a type can be invoked (as if by std::invoke) with the given argument types (class template) |
|---|
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