Vicente J. Botet Escriba wrote:
I have the impression that mp11 cannot use the meta function returned by a function as a parameter of an algorithm, but I'm missing something that it should be evident to you. How can we define a compose meta-function that could be used later as parameter?
This is a metafunction in mp11: template<class... T> using F = /*...*/; This is a quoted metafunction: struct Q { template<class... T> using invoke = /*...*/ }; Since quoted metafunctions are types, you can operate on them (although mp11 doesn't yet provide any built-in means to compose them), but to pass one to an algorithm, you need mp_transform<List, Q::invoke> instead of just mp_transform<List, F>
I just find it weird to take std::variant as a data type that models type list.
The need to operate on the list of variant alternatives is actually pretty common. Hence std::variant_size (which is just mp_size in mp11), std::variant_alternative_t (mp_at_c). Similarly std::tuple_size, std::tuple_element_t. This endless reinvention of the wheel is completely unnecessary.