On Sun, Mar 19, 2017 at 9:29 PM, Peter Dimov via Boost < boost@lists.boost.org> wrote:
Bruno Dutra wrote:
It would be possible in principle to make the algorithms take > mpl::vector and return mp_list, I suppose.
You forgot to take into account that algorithms such as mpl::insert and mpl::erase return proxies that inherit from vectors and don't expose the elements in their types signatures, while being themselves valid instances of a Vector. This is the real deal breaker.
On MSVC, insert/erase return numbered vectors, but on g++ and clang++, you're right, they return some weird v_item sequences.
What is our use case here though? From where would those mpl types come?
I don't have a use case, I'm just trying to argue against the idea of implementing any implicit native support for MPL sequences, which besides non-trivial is also fruitless. Moreover, providing support for numbered instances of mpl::vector only and not for its proxies would really be a bad idea, because it doesn't solve the common use case, where the user has some legacy metaprogram that manipulates mpl::vectors, certainly also through insert and erase, and wants to pass this on to the algorithms of a new library that advertises itself as interoperating with MPL natively, only to realize the hard way that it doesn't really. I stand by the opinion that it can't go wrong with explicit converters. Bruno