std::move_only_function::operator()
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< cpp | utility | functional | move only function
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R operator()( Args... args ) /*cv*/ /*ref*/ noexcept(/*noex*/);
(since C++23)
Invokes the stored callable target with the parameters args. The /*cv*/, /*ref*/, and /*noex*/ parts of operator() are identical to those of the template parameter of std::move_only_function.
Equivalent to return std::invoke_r <R>(/*cv-ref-cast*/(f), std::forward <Args>(args)...);, where f is a cv-unqualified lvalue that denotes the target object of *this, and /*cv-ref-cast*/(f) is equivalent to:
- f if cv ref is either empty or &, or
- std::as_const (f) if cv ref is either const or const &, or
- std::move(f) if cv ref is &&, or
- std::move(std::as_const (f)) if cv ref is const &&.
The behavior is undefined if *this is empty.
[edit] Parameters
args
-
parameters to pass to the stored callable target
[edit] Return value
std::invoke_r <R>(/*cv-ref-cast*/(f), std::forward <Args>(args)...).
[edit] Exceptions
Propagates the exception thrown by the underlying function call.
[edit] Example
The following example shows how std::move_only_function can passed to other functions by value. Also, it shows how std::move_only_function can store lambdas.
Run this code
#include <iostream> #include <functional> void call(std::move_only_function <int() const> f) // can be passed by value { std::cout << f() << '\n'; } int normal_function() { return 42; } int main() { int n = 1; auto lambda = [&n](){ return n; }; std::move_only_function <int() const> f = lambda; call(std::move(f)); n = 2; call(lambda); f = normal_function; call(std::move(f)); }
Output:
1 2 42