On Sun, 2024-09-29 at 16:00 -0500, Barry Revzin via Std-Proposals
wrote:
>
>
> On Sun, Sep 29, 2024 at 3:32 PM Arthur O'Dwyer via Std-Proposals
> <std-proposals_at_[hidden]> wrote:
> > On Sun, Sep 29, 2024 at 3:26 PM Avi Kivity via Std-Proposals
> > <std-proposals_at_[hidden]> wrote:
> > > I find it common to want to constrain a range to return a
> > > particular type. Something like
> > >
> > > void f(std::ranges::range_of<unsigned> auto&&
> > > range_of_unsigned) { ... }
> > >
> > > It would be trivial to define such a concept, or to forego the
> > > abbreviated template syntax and use a requires clause, but it
> > > seems to me this should be a vocabulary concept.
> > > There's the question of whether the type should be same_as or
> > > convertible_to, perhaps there is room for two concepts here.
> > >
> >
> >
> > This sounds like the same thing (in practice) as the exposition-
> > only container-compatible-range [1].
> >
>
>
> The problem with range_of is what exactly that should mean. Should
> range_of<unsigned> actually match any range of integral (i.e.
> convertible_to) or just specifically ranges of prvalue unsigned (i.e.
> same_as)? But same_as wouldn't even match vector<unsigned>, so if you
> want that did you actually want same_as but matching on value_type
> instead? Or decays_to?

Why would same_as not match vector<unsigned>? Of course we'd match
value_type, not the range itself.


>
> So... sure, container-compatible-range is one of those things. But
> the problem with range_of<T> is what exactly you wanted to check your
> T against.
>

We'd just have two concepts. Maybe range_of (with convertible_to
matching, used for reads) and range_of_exactly (used for writes). I'd
say range_of is much more useful.

[1] container-compatible-range
    https://eel.is/c++draft/container.intro.reqmts#concept:container-compatible-range