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libstdc++: Fix constraint recursion in basic_const_iterator operator- [PR115046]

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It was proposed in PR112490 to also adjust basic_const_iterator's friend
operator-(sent, iter) overload alongside the r15-7757-g4342c50ca84ae5
adjustments to its comparison operators, but we lacked a concrete
testcase demonstrating fixable constraint recursion there.  It turns out
Hewill Kang's PR115046 is such a testcase!  So this patch makes the same
adjustments to that overload as well, fixing PR115046.  The LWG 4218 P/R
will need to get adjusted too.

	PR libstdc++/115046
	PR libstdc++/112490

libstdc++-v3/ChangeLog:

	* include/bits/stl_iterator.h (basic_const_iterator::operator-):
	Replace non-dependent basic_const_iterator function parameter with
	a dependent one of type basic_const_iterator<_It2> where _It2
	matches _It.
	* testsuite/std/ranges/adaptors/as_const/1.cc (test04): New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
This commit is contained in:
Patrick Palka 2025-04-09 17:48:05 -04:00
parent f3862ab079
commit d69f73c033
2 changed files with 15 additions and 2 deletions
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4
libstdc++-v3/include/bits/stl_iterator.h
View file

@ -2933,10 +2933,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
noexcept(noexcept(_M_current - __y))
{ return _M_current - __y; }
template<__detail::__not_a_const_iterator _Sent>
template<__detail::__not_a_const_iterator _Sent, same_as<_It> _It2>
requires sized_sentinel_for<_Sent, _It>
friend constexpr difference_type
operator-(const _Sent& __x, const basic_const_iterator& __y)
operator-(const _Sent& __x, const basic_const_iterator<_It2>& __y)
noexcept(noexcept(__x - __y._M_current))
{ return __x - __y._M_current; }

13
libstdc++-v3/testsuite/std/ranges/adaptors/as_const/1.cc
View file

@ -69,10 +69,23 @@ test03()
auto r2 = views::as_const(views::all(v));
}
void
test04()
{
// PR libstdc++/115046 - meta-recursion with join_view and as_const_view
int x[3] = {1,2,3};
auto v = x
| views::chunk(3)
| views::transform(views::as_const)
| views::join;
VERIFY( ranges::equal(v, x) );
}
int
main()
{
static_assert(test01());
static_assert(test02());
test03();
test04();
}