Difference between revisions of "cpp/named req/Callable"
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Revision as of 00:29, 20 March 2017
Template:cpp/concept/title Template:cpp/concept/navbar
A Template:concept 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)
Contents |
Requirements
The type T
satisfies Callable
if
Given
-
f
, an object of typeT
-
ArgTypes
, suitable list of argument types -
R
, suitable return type
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:
- if
f
is a pointer to member function of classT
:
- If std::is_base_of<T, std::decay_t<decltype(t1)>>::value is true, then INVOKE(f, t1, t2, ..., tN) is equivalent to (t1.*f)(t2, ..., tN)
- otherwise, if std::decay_t<decltype(t1)> is a specialization of std::reference_wrapper, then INVOKE(f, t1, t2, ..., tN) is equivalent to (t1.get().*f)(t2, ..., tN)(since C++17)
- otherwise, if
t1
does not satisfy the previous items, then INVOKE(f, t1, t2, ..., tN) is equivalent to ((*t1).*f)(t2, ..., tN).
- otherwise, if N == 1 and
f
is a pointer to data member of classT
:
- If std::is_base_of<T, std::decay_t<decltype(t1)>>::value is true, then INVOKE(f, t1) is equivalent to t1.*f
- otherwise, if std::decay_t<decltype(t1)> is a specialization of std::reference_wrapper, then INVOKE(f, t1) is equivalent to t1.get().*f(since C++17)
- otherwise, if
t1
does not satisfy the previous items, then INVOKE(f, t1) is equivalent to (*t1).*f
- otherwise, INVOKE(f, t1, t2, ..., tN) is equivalent to f(t1, t2, ..., tN) (that is,
f
is a Template:concept)
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 Template:concept type (not just Template:concept)
std::function | |
std::bind | |
std::result_of | |
std::thread::thread | |
std::call_once | |
std::async | |
std::packaged_task | |
std::reference_wrapper |
See also
checks if a type can be invoked (as if by std::invoke) with the given argument types (class template) |