Re: [review][fixed_string] End of review period approaching and a plea

From: Peter Dimov (pdimov_at_[hidden])
Date: 2019-12-04 18:44:21

Andrey Semashev wrote:
> On 2019-12-04 18:24, Alexander Grund via Boost wrote:
> >
> >> I would hope to see close to the same semantics as std::array<T,0>, 
> >> which I believe allows data() to return nullptr.
> >
> > I don't think so:
> >
> > "There is a special case for a zero-length array (|N == 0|). In that 
> > case, array.begin() == array.end(), which is some unique value. The 
> > effect of calling front() or back() on a zero-sized array is undefined." 
> > from https://en.cppreference.com/w/cpp/container/array
> >
> > IMO this excludes nullptr as that won't be unique
>
> I don't think iterators from different instances of a container are 
> comparable. IOW, "unique" means distinct from any possible values of valid 
> iterators obtained from this particular container instance.
>
> That might not apply to pointers, though.

Pointers are comparable with ==, and array<T, 0> usually returns 
reinterpret_cast<T*>(this) from data() to satisfy the uniqueness 
requirement.

Or used to return - I see that libstdc++ returns nullptr now, probably 
because reinterpret_cast can't be constexpr.

https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/std/array#L76