#### any_completion_handler::operator()

Function call operator.

    template<
        typename... Args>
    auto operator()(
        Args &&... args);

Invokes target completion handler with the supplied arguments.

This function may only be called once, as the target handler is moved from. The polymorphic wrapper is left in an empty state.

Throws `std::bad_function_call` if the polymorphic wrapper is empty.