Resolves LWG4096, views::iota(views::iota(0)) should be rejected.
For __e of type _Tp that is specialization of iota_view, the CTAD based
expression iota_view(__e) is well formed, and creates a copy of __e.
As iota_view<decay_t<_Tp>> is ill-formed in this case (iota_view is not
weakly_incrementable), using that type in return type explicitly, removes
the overload from overload resolution in this case.
The (now redudant) __detail::__can_iota_view constrain in template head is
preserved, to provide error messages consistent with adaptors for other
non-incrementable types.
libstdc++-v3/ChangeLog:
* include/std/ranges (_Iota::operator()(_Tp&&)): Replace
auto return type and CTAD with iota_view<decay_t<_Tp>>.
* testsuite/std/ranges/iota/iota_view.cc: Tests if
views::iota(iota_view) is rejected.
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
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