https://gcc.gnu.org/g:7f7f1878eedd8093d382e1e7b74649d7e97d5918
commit r16-3576-g7f7f1878eedd8093d382e1e7b74649d7e97d5918
Author: Patrick Palka <ppa...@redhat.com>
Date: Thu Sep 4 09:57:36 2025 -0400
libstdc++: Conditionalize LWG 3569 changes to join_view
LWG 3569 adjusted join_view's iterator specification to handle non
default-constructible iterators by wrapping the corresponding data member
in std::optional, which we followed suit in r13-2649-g7aa80c82ecf3a3.
But this wrapping is unnecessary for iterators that are already
default-constructible. Rather than unconditionally using std::optional
here, which introduces time/space overhead, this patch conditionalizes
our LWG 3569 changes on the iterator in question being non-forward (and
thus non default-constructible). We check forwardness instead of
default-constructibility in order to accommodate input-only iterators
that satisfy but do not model default_initializable, e.g. whose default
constructor is underconstrained.
libstdc++-v3/ChangeLog:
* include/std/ranges (join_view::_Iterator::_M_satisfy):
Adjust to handle non-std::optional _M_inner as per before LWG 3569.
(join_view::_Iterator::_M_get_inner): New.
(join_view::_Iterator::_M_inner): Don't wrap in std::optional if
the iterator is forward. Initialize.
(join_view::_Iterator::operator*): Use _M_get_inner instead
of *_M_inner.
(join_view::_Iterator::operator++): Likewise.
(join_view::_Iterator::iter_move): Likewise.
(join_view::_Iterator::iter_swap): Likewise.
Reviewed-by: Tomasz Kamiński <tkami...@redhat.com>
Reviewed-by: Jonathan Wakely <jwak...@redhat.com>
Diff:
---
libstdc++-v3/include/std/ranges | 49 +++++++++++++++++++++++++++++++----------
1 file changed, 37 insertions(+), 12 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 156d12b31ba1..bae50d06ca81 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2889,7 +2889,12 @@ namespace views::__adaptor
}
if constexpr (_S_ref_is_glvalue)
- _M_inner.reset();
+ {
+ if constexpr (forward_iterator<_Inner_iter>)
+ _M_inner = _Inner_iter();
+ else
+ _M_inner.reset();
+ }
}
static constexpr auto
@@ -2929,6 +2934,24 @@ namespace views::__adaptor
return *_M_parent->_M_outer;
}
+ constexpr _Inner_iter&
+ _M_get_inner()
+ {
+ if constexpr (forward_iterator<_Inner_iter>)
+ return _M_inner;
+ else
+ return *_M_inner;
+ }
+
+ constexpr const _Inner_iter&
+ _M_get_inner() const
+ {
+ if constexpr (forward_iterator<_Inner_iter>)
+ return _M_inner;
+ else
+ return *_M_inner;
+ }
+
constexpr
_Iterator(_Parent* __parent, _Outer_iter __outer) requires
forward_range<_Base>
: _M_outer(std::move(__outer)), _M_parent(__parent)
@@ -2942,7 +2965,9 @@ namespace views::__adaptor
[[no_unique_address]]
__detail::__maybe_present_t<forward_range<_Base>, _Outer_iter>
_M_outer
= decltype(_M_outer)();
- optional<_Inner_iter> _M_inner;
+ __conditional_t<forward_iterator<_Inner_iter>,
+ _Inner_iter, optional<_Inner_iter>> _M_inner
+ = decltype(_M_inner)();
_Parent* _M_parent = nullptr;
public:
@@ -2966,7 +2991,7 @@ namespace views::__adaptor
constexpr decltype(auto)
operator*() const
- { return **_M_inner; }
+ { return *_M_get_inner(); }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3500. join_view::iterator::operator->() is bogus
@@ -2974,7 +2999,7 @@ namespace views::__adaptor
operator->() const
requires __detail::__has_arrow<_Inner_iter>
&& copyable<_Inner_iter>
- { return *_M_inner; }
+ { return _M_get_inner(); }
constexpr _Iterator&
operator++()
@@ -2985,7 +3010,7 @@ namespace views::__adaptor
else
return *_M_parent->_M_inner;
}();
- if (++*_M_inner == ranges::end(__inner_range))
+ if (++_M_get_inner() == ranges::end(__inner_range))
{
++_M_get_outer();
_M_satisfy();
@@ -3015,9 +3040,9 @@ namespace views::__adaptor
{
if (_M_outer == ranges::end(_M_parent->_M_base))
_M_inner = ranges::end(__detail::__as_lvalue(*--_M_outer));
- while (*_M_inner == ranges::begin(__detail::__as_lvalue(*_M_outer)))
- *_M_inner = ranges::end(__detail::__as_lvalue(*--_M_outer));
- --*_M_inner;
+ while (_M_get_inner() ==
ranges::begin(__detail::__as_lvalue(*_M_outer)))
+ _M_get_inner() = ranges::end(__detail::__as_lvalue(*--_M_outer));
+ --_M_get_inner();
return *this;
}
@@ -3044,14 +3069,14 @@ namespace views::__adaptor
friend constexpr decltype(auto)
iter_move(const _Iterator& __i)
- noexcept(noexcept(ranges::iter_move(*__i._M_inner)))
- { return ranges::iter_move(*__i._M_inner); }
+ noexcept(noexcept(ranges::iter_move(__i._M_get_inner())))
+ { return ranges::iter_move(__i._M_get_inner()); }
friend constexpr void
iter_swap(const _Iterator& __x, const _Iterator& __y)
- noexcept(noexcept(ranges::iter_swap(*__x._M_inner, *__y._M_inner)))
+ noexcept(noexcept(ranges::iter_swap(__x._M_get_inner(),
__y._M_get_inner())))
requires indirectly_swappable<_Inner_iter>
- { return ranges::iter_swap(*__x._M_inner, *__y._M_inner); }
+ { return ranges::iter_swap(__x._M_get_inner(), __y._M_get_inner()); }
friend _Iterator<!_Const>;
template<bool> friend struct _Sentinel;
