22 General utilities library [utilities]

22.10 Function objects [function.objects]

22.10.17 Polymorphic function wrappers [func.wrap] Move-only wrapper [func.wrap.move] Invocation [func.wrap.move.inv]

explicit operator bool() const noexcept;
Returns: true if *this has a target object, otherwise false.
R operator()(ArgTypes... args) cv ref noexcept(noex);
Preconditions: *this has a target object.
Effects: Equivalent to: return INVOKE<R>(static_cast<F inv-quals>(f), std::forward<ArgTypes>(args)...); where f is an lvalue designating the target object of *this and F is the type of f.