2.6 KiB
[func.wrap.move.class]
22 General utilities library [utilities]
22.10 Function objects [function.objects]
22.10.17 Polymorphic function wrappers [func.wrap]
22.10.17.4 Move-only wrapper [func.wrap.move]
22.10.17.4.2 Class template move_only_function [func.wrap.move.class]
namespace std {template<class R, class... ArgTypes>class move_only_function<R(ArgTypes...) cv ref noexcept(noex)> {public:using result_type = R; // [func.wrap.move.ctor], constructors, assignments, and destructor move_only_function() noexcept; move_only_function(nullptr_t) noexcept; move_only_function(move_only_function&&) noexcept; template move_only_function(F&&); template<class T, class... Args>explicit move_only_function(in_place_type_t, Args&&...); template<class T, class U, class... Args>explicit move_only_function(in_place_type_t, initializer_list, Args&&...);
move_only_function& operator=(move_only_function&&); move_only_function& operator=(nullptr_t) noexcept; template move_only_function& operator=(F&&); ~move_only_function(); // [func.wrap.move.inv], invocationexplicit operator bool() const noexcept; R operator()(ArgTypes...) cv ref noexcept(noex); // [func.wrap.move.util], utilityvoid swap(move_only_function&) noexcept; friend void swap(move_only_function&, move_only_function&) noexcept; friend bool operator==(const move_only_function&, nullptr_t) noexcept; private:templatestatic constexpr bool is-callable-from = see below; // exposition only};}
The move_only_function class template provides polymorphic wrappers that generalize the notion of a callable object ([func.def]).
These wrappers can store, move, and call arbitrary callable objects, given a call signature.
Recommended practice: Implementations should avoid the use of dynamically allocated memory for a small contained value.
[Note 1:
Such small-object optimization can only be applied to a type T for which is_nothrow_move_constructible_v is true.
â end note]