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Rationale for changes to disambiguation types
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Daniel
Dec 15, 2019, 9:17:12 AM12/15/19
to
In C++ 2017, the disambiguation tag type allocator_arg_t has been redefined from
struct allocator_arg_t {}; // (*)
to
struct allocator_arg_t { explicit allocator_arg_t() = default; }; // (**)
New disambiguation tag types introduced with 2017, e.g. in_place_t, have the same form as (**). Was there a technical reason for the change that I'm not
seeing?
Thanks,
Daniel
struct allocator_arg_t {}; // (*)
to
struct allocator_arg_t { explicit allocator_arg_t() = default; }; // (**)
New disambiguation tag types introduced with 2017, e.g. in_place_t, have the same form as (**). Was there a technical reason for the change that I'm not
seeing?
Thanks,
Daniel
Öö Tiib
Dec 15, 2019, 9:40:36 AM12/15/19
to
producible from nothing (like from {}) makes no sense and defeats the
purpose of those.
It was defect 2510. "Tag types should not be DefaultConstructible"
<http://cplusplus.github.io/LWG/lwg-defects.html#2510>
Daniel
Dec 15, 2019, 10:27:32 AM12/15/19
to
On Sunday, December 15, 2019 at 9:40:36 AM UTC-5, Öö Tiib wrote:
> On Sunday, 15 December 2019 16:17:12 UTC+2, Daniel wrote:
> > In C++ 2017, the disambiguation tag type allocator_arg_t has been redefined from
> >
> > struct allocator_arg_t {}; // (*)
> >
> > to
> >
> > struct allocator_arg_t { explicit allocator_arg_t() = default; }; // (**)
> >
>
> On Sunday, 15 December 2019 16:17:12 UTC+2, Daniel wrote:
> > In C++ 2017, the disambiguation tag type allocator_arg_t has been redefined from
> >
> > struct allocator_arg_t {}; // (*)
> >
> > to
> >
> > struct allocator_arg_t { explicit allocator_arg_t() = default; }; // (**)
> >
>
> It was defect 2510. "Tag types should not be DefaultConstructible"
> <http://cplusplus.github.io/LWG/lwg-defects.html#2510>
Thanks,
> <http://cplusplus.github.io/LWG/lwg-defects.html#2510>
Daniel
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