Consider adding remove_member_cv_ref and copy_member_cv_ref

[ldionne]

Taken from https://lists.boost.org/Archives/boost/2017/04/234374.php:

In "member qualifier features", I'm missing remove_member_cv_ref (obvious semantics) and copy_member_cv_ref (copies cv+ref from one member pointer to another.)

and your reply in https://lists.boost.org/Archives/boost/2017/04/234446.php:

I'm slightly hesitant to add remove_member_cv_ref (remove_member_qualifiers?), because it doesn't quite mirror <type_traits>. Would this also remove noexcept/transaction_safe? I'm conflicted about copy_member_cv_ref, because I'm not sure whether it would be more useful to copy them to a function type or value type.

[pdimov]

I admit I don't have a use case for copy_member_cv_ref, so take this suggestion with a grain of salt. copy_cv is often useful for types (T cv, U -> U cv), but the analogy may not hold here.

[willwray]

FYI I have a use case for copy_member_qualifiers including noexcept along with cv/ref (so the target then has to be a function type).

My application is type reflection where each C++ compound has a reflected version (denoted here with a capital or capitalised acronym):

1. type -> Type
2. type const -> CV<Type const>
3. type& -> Ref<Type&>
4. ret(args...) const && noexcept -> Fun<Ret(Args...) const && noexcept>

(2) needs a copy_cv, (3) needs a copy_ref and (4) needs this copy_cvref_noexcept

Using the actual qualifiers in the reflected type saves inventing a scheme for encoding and decoding the qualifiers.

This is just FYI, not a request to add this trait to callable_traits.