Proposal mp_eval_and?

[HDembinski]

This is a combination of mp_eval_if and mp_and. mp_and already shortcuts on the first substitution failure when mp_to_bool is applied to T or when the application yields mp_false. mp_eval_and would provide the same functionality for applications of meta functions F... on T.

template <class T, template<class>class F...> using mp_eval_and = ...

mp_eval_and<T, F0, F1, ...> is mp_false, if F0<T> is mp_false or a substitution failure. Otherwise it is mp_eval_and<T, F1, ...> and so on.

Example application for mp_eval_and

template <class T>
using is_unsigned_integral = mp_eval_and<T, std::is_integral, std::is_unsigned>;

[pdimov]

Is this the one-liner

template<class T, template<class...> class... F> using mp_eval_and = mp_and<F<T>...>;

?

[HDembinski]

I just tried it out, the one-liner seems to work, although I don't get why. I thought the right hand side mp_and<F<T>> would cause a substitution failure if F<T> is a substitution failure. mp_eval_and should never cause a substitution failure.

[HDembinski]

I have an implementation here: https://github.com/HDembinski/mp11/tree/mp_eval_and, pieced together from looking at how you do things.

[pdimov]

In your example, F0 is is_integral, and is_integral<T> is never a substitution failure, because it's a struct. F0<T>::value can be a substitution failure, but it's eaten by mp_and.

[HDembinski]

Ok, then my example is just bad and my understanding of your one-liner was correct at least.

[HDembinski]

I am closing this as it seems superfluous.