Function wrap

dlib/test/invoke.cpp:495–507

          std::enable_if_t<is_callable<Callable>::value, bool> = true,
          std::enable_if_t<callable_nargs<Callable>::value >= 1, bool> = true,
          std::enable_if_t<std::is_floating_point<callable_arg<0, Callable>>::value, bool> = true
        >
        auto wrap (
            Callable&& clb,
            int& i
        )
        {
            i = 1;

            return [pclb = std::forward<Callable>(clb)](float a, int b, long c) {
                pclb(a, b, c);
            };
        }

        template <
          class Callable,