https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96042
Bug ID: 96042
Summary: Reference type of std::ranges::iota is __int128 with
-std=c++2a?!
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc-bugs at marehr dot dialup.fu-berlin.de
Target Milestone: ---
The following code
```c++
#include <ranges>
using iota_view = std::ranges::iota_view<size_t>;
using reference_t = std::ranges::range_difference_t<iota_view>;
static_assert(std::same_as<reference_t, __int128>); // why?
// but std::numeric_limits is not specialised which indicates that we use
__STRICT_ANSI__
using t = std::numeric_limits<__int128>;
static_assert(t::is_specialized);
```
https://godbolt.org/z/-XFyYN
I don't fully understand what `__int128` and `__STRICT_ANSI__` means, but I
think it is unexpected that I get a type that is not described in the standard.
I know that `std::indirectly_readable` allows (compiler) implementation defined
signed integer types, but from what I have seen, `__int128` is normally only
supported / exposed in the gnu standard library if `__STRICT_ANSI__` is not
defined.
Since `-std=c++2a` does not provide a specialisation for `std::numeric_limits`,
I assume that this means, that `__STRICT_ANSI__` is not defined in that mode,
and I think this is inconsistent behaviour.
Related issues in the range-v3 library:
* https://github.com/ericniebler/range-v3/issues/1514
* https://github.com/ericniebler/range-v3/issues/1516
