[PATCH] PR libstdc++/80939 Remove unmeetable constexpr specifiers

[Tim Shen via libstdc++]

On Fri, Jun 2, 2017 at 6:07 AM, Jonathan Wakely wrote:
> As the PR points out, we aren't qualifying calls to __ref_cast, and
> have 'constexpr' on function templates that can never be usable in
> constant expressions.

Apology for the constexpr trolling, but that was not intentional. :)

I'm curious why no tests break. Is it because constexpr in a template
function is a no-op instead of a hard error, when the function
definition is not constexpr?

The patch looks good.

>
> This fixes it, and also simplifies __variant::__erased_dtor by using
> std::_Destroy, although that requires including quite a lot more code,
> for iterator_traits and allocator_traits.  If that matters (probably
> not) then <bits/stl_construct.h> could be split up to move _Construct
> and _Destroy to a new <bits/stl_construct_base.h>.  Or maybe I should
> just leave __erased_dtor alone (apart from qualifying the __ref_cast
> call).
>
> Anybody feel strongly either way?
>
>         PR libstdc++/80939
>         * include/std/variant (__erased_ctor, __erased_assign,
> __erased_swap)
>         (__erased_hash): Remove constexpr specifier and qualify calls to
>         __ref_cast.
>         (__erased_dtor): Remove constexpr specifier and use _Destroy.
>
>



-- 
Regards,
Tim Shen