Function map

tutorials/external/catch.hpp:3864–3868

    template <typename Func, typename U, typename T = MapFunctionReturnType<Func, U>>
    GeneratorWrapper<T> map(Func&& function, GeneratorWrapper<U>&& generator) {
        return GeneratorWrapper<T>(
            pf::make_unique<MapGenerator<T, U, Func>>(std::forward<Func>(function), std::move(generator))
        );
    }

    template <typename T, typename U, typename Func>
    GeneratorWrapper<T> map(Func&& function, GeneratorWrapper<U>&& generator) {