On Thu, 25 Jun 2026 at 13:31, Tomasz Kamiński <[email protected]> wrote:
>
> This implements remaining changes from P3612R1 Harmonize proxy-reference
> operations (LWG 3638 and 4187).
>
> As the const-assigment operator in bitset::reference (from LWG4187)
> is used by range concepts (std::indirectly_writable) to recognize
> iterator returning it by value as proxy iterator (see range_proxy.cc) test,
> this change is backported to C++23. This puts it inline with vector<bool>
> reference and other proxy type, for which the coresponding assigment
> operator where added by P2321 in C++20 and implemented in r13-2159-g72886f.
>
> Similary, a swap overloads accepting bitset::reference by value and bool&,
> are necessary for ranges::swap and ranges::iter_swap to work correctly,
> so they should also backported. This patch follows the approach from
> resolution of LWG3638 from r12-5311-g59434931fb658f, and backports the
> overloads to C++11. This harmonizes the operations on this two proxy
> types (per paper title). Corresponding test are added to both classes.
>
> The deprecation warning for static vector<bool>::swap is added sinc C++26.
> The text in _GLIBCXX26_DEPRECATED_SUGGEST leads to following message:
> 'static constexpr void std::vector<bool, _Alloc>::swap(reference, reference)
> [with... ]' is deprecated: use 'swap' invoked via ADL or 'std::ranges::swap'
> instead
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/stl_bvector.h: Add _GLIBCXX_RESOLVE_LIB_DEFECTS
> comment for 3638.
> (vector<bool, _Alloc>::swap): Add deprected attribute via
> _GLIBCXX26_DEPRECATED_SUGGEST.
> * include/std/bitset (bitset::operator=(bool) const)
> [__cplusplus > 202002]: Define.
> (bistset::reference::swap) [__cplusplus >= 201103L]: Define.
> * testsuite/20_util/bitset/access/range_proxy.cc: New test.
> * testsuite/20_util/bitset/access/ref_swap.cc: New test.
> * testsuite/23_containers/vector/bool/element_access/range_proxy.cc:
> New test.
> * testsuite/23_containers/vector/bool/element_access/ref_swap.cc:
> New test.
> * testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc:
> Checkfor deprecated warning on static swap.
> ---
> Do you agree with my backport choice for swap? I think the minimum is
> since C++23.
I don't remember why I chose C++11 for the swap overloads for
vector<bool>::reference, but being consistent with that makes sense.
>
> Testing on x86_64-linux. *bitset* and *vector/bool* test already passed
> in all standard modes. OK for trunk?
>
> libstdc++-v3/include/bits/stl_bvector.h | 4 +
> libstdc++-v3/include/std/bitset | 43 +++++++++
> .../20_util/bitset/access/range_proxy.cc | 94 +++++++++++++++++++
> .../20_util/bitset/access/ref_swap.cc | 28 ++++++
> .../vector/bool/element_access/range_proxy.cc | 62 ++++++++++++
> .../vector/bool/element_access/ref_swap.cc | 38 ++++++++
> .../vector/bool/modifiers/swap/constexpr.cc | 2 +-
> 7 files changed, 270 insertions(+), 1 deletion(-)
> create mode 100644
> libstdc++-v3/testsuite/20_util/bitset/access/range_proxy.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/bitset/access/ref_swap.cc
> create mode 100644
> libstdc++-v3/testsuite/23_containers/vector/bool/element_access/range_proxy.cc
> create mode 100644
> libstdc++-v3/testsuite/23_containers/vector/bool/element_access/ref_swap.cc
>
> diff --git a/libstdc++-v3/include/bits/stl_bvector.h
> b/libstdc++-v3/include/bits/stl_bvector.h
> index f190d1be5ce..0637e687cbb 100644
> --- a/libstdc++-v3/include/bits/stl_bvector.h
> +++ b/libstdc++-v3/include/bits/stl_bvector.h
> @@ -149,6 +149,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> { *_M_p ^= _M_mask; }
>
> #if __cplusplus >= 201103L
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 3638. vector<bool>::swap(reference, reference) is useless
> +
> _GLIBCXX20_CONSTEXPR
> friend void
> swap(_Bit_reference __x, _Bit_reference __y) noexcept
> @@ -1266,6 +1269,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> }
>
> // [23.2.5]/1, third-to-last entry in synopsis listing
> + _GLIBCXX26_DEPRECATED_SUGGEST("swap' invoked via ADL or
> 'std::ranges::swap")
> _GLIBCXX20_CONSTEXPR
> static void
> swap(reference __x, reference __y) _GLIBCXX_NOEXCEPT
> diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
> index a8cb337f4b1..a5822319b90 100644
> --- a/libstdc++-v3/include/std/bitset
> +++ b/libstdc++-v3/include/std/bitset
> @@ -908,6 +908,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> return *this;
> }
>
> +#if __cplusplus > 202002L
Should we use __glibcxx_ranges_zip here? That's the macro for P2321
which is what made the const-assignable changes that motivate this
change.
If it's changed here it should be changed in the range_proxy.cc test too.
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 4187. bitset::reference should be const-assignable
> + constexpr const reference&
> + operator=(bool __x) const noexcept
> + {
> + if (__x)
> + *_M_wp |= _Base::_S_maskbit(_M_bpos);
> + else
> + *_M_wp &= ~_Base::_S_maskbit(_M_bpos);
> + return *this;
> + }
> +#endif // C++23
> +
> // For b[i] = b[__j];
> _GLIBCXX23_CONSTEXPR
> reference&
> @@ -939,6 +953,35 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> *_M_wp ^= _Base::_S_maskbit(_M_bpos);
> return *this;
> }
> +
> +#if __cplusplus >= 201103L
Using 201103 here matches the condition for the
vector<bool>::reference swap overloads, good.
> + _GLIBCXX23_CONSTEXPR
> + friend void
> + swap(reference __x, reference __y) noexcept
> + {
> + bool __tmp = __x;
> + __x = __y;
> + __y = __tmp;
> + }
> +
> + _GLIBCXX23_CONSTEXPR
> + friend void
> + swap(reference __x, bool& __y) noexcept
> + {
> + bool __tmp = __x;
> + __x = __y;
> + __y = __tmp;
> + }
> +
> + _GLIBCXX23_CONSTEXPR
> + friend void
> + swap(bool& __x, reference __y) noexcept
> + {
> + bool __tmp = __x;
> + __x = __y;
> + __y = __tmp;
> + }
> +#endif
> };
> friend class reference;
>
> diff --git a/libstdc++-v3/testsuite/20_util/bitset/access/range_proxy.cc
> b/libstdc++-v3/testsuite/20_util/bitset/access/range_proxy.cc
> new file mode 100644
> index 00000000000..9eac384ce44
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/bitset/access/range_proxy.cc
> @@ -0,0 +1,94 @@
> +// { dg-do run { target c++20 } }
> +
> +#include <bitset>
> +#include <concepts>
> +#include <iterator>
> +#include <testsuite_hooks.h>
> +
> +void
> +test_swap()
> +{
> + std::bitset<2> v("01");
> + std::ranges::swap(v[0], v[1]);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true;
> + std::ranges::swap(v[0], b);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + std::ranges::swap(b, v[1]);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +template<size_t N>
> +struct bitset_iterator
> +{
> + using value_type = bool;
> + using reference = std::bitset<2>::reference;
> + using iterator_category = std::forward_iterator_tag;
> + using difference_type = std::ptrdiff_t;
> +
> + bitset_iterator() = default;
> + bitset_iterator(std::bitset<N>& c) noexcept : cont(&c) {}
> +
> + reference operator*() const noexcept
> + { return (*cont)[pos]; }
> +
> + bitset_iterator& operator++() {
> + ++pos;
> + return *this;
> + }
> +
> + bitset_iterator operator++(int) {
> + auto tmp = *this;
> + ++pos;
> + return *this;
> + };
> +
> + friend bool operator==(bitset_iterator, bitset_iterator) = default;
> +
> +private:
> + std::bitset<N>* cont = nullptr;
> + size_t pos = 0;
> +};
> +
> +void
> +test_iter_swap()
> +{
> + std::bitset<2> v("01");
> + auto it1 = bitset_iterator<2>(v);
> + auto it2 = std::ranges::next(it1);
> + std::ranges::iter_swap(it1, it2);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true, *p = &b;
> + std::ranges::iter_swap(it1, p);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + std::ranges::iter_swap(p, it2);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +#if __cplusplus > 202002L
> +static_assert( std::indirectly_writable<bitset_iterator<2>, bool> );
> +static_assert( std::indirectly_writable<bitset_iterator<2>,
> + std::bitset<2>::reference> );
> +
> +#else
> +static_assert( !std::indirectly_writable<bitset_iterator<2>, bool> );
> +static_assert( !std::indirectly_writable<bitset_iterator<2>,
> + std::bitset<2>::reference> );
> +#endif
> +
> +int
> +main()
> +{
> + test_swap();
> + test_iter_swap();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/bitset/access/ref_swap.cc
> b/libstdc++-v3/testsuite/20_util/bitset/access/ref_swap.cc
> new file mode 100644
> index 00000000000..1d8e3c1bf49
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/bitset/access/ref_swap.cc
> @@ -0,0 +1,28 @@
> +// { dg-do run { target c++11 } }
> +
> +#include <bitset>
> +#include <testsuite_hooks.h>
> +
> +void
> +test_friend()
> +{
> + std::bitset<2> v("01");
> + swap(v[0], v[1]);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true;
> + swap(v[0], b);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + swap(b, v[1]);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +int
> +main()
> +{
> + test_friend();
> +}
> diff --git
> a/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/range_proxy.cc
>
> b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/range_proxy.cc
> new file mode 100644
> index 00000000000..075132034f1
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/range_proxy.cc
> @@ -0,0 +1,62 @@
> +// { dg-do run { target c++20 } }
> +
> +#include <vector>
> +#include <concepts>
> +#include <iterator>
> +#include <testsuite_hooks.h>
> +
> +void
> +test_swap()
> +{
> + std::vector<bool> v{true, false};
> + std::ranges::swap(v[0], v[1]);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true;
> + std::ranges::swap(v[0], b);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + std::ranges::swap(b, v[1]);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +void
> +test_iter_swap()
> +{
> + std::vector<bool> v{true, false};
> + auto it1 = v.begin();
> + auto it2 = std::ranges::next(it1);
> + std::ranges::iter_swap(it1, it2);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true, *p = &b;
> + std::ranges::iter_swap(it1, p);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + std::ranges::iter_swap(p, it2);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +#if __cplusplus > 202002L
> +static_assert( std::indirectly_writable<std::vector<bool>::iterator, bool> );
> +static_assert( std::indirectly_writable<std::vector<bool>::iterator,
> + std::vector<bool>::reference> );
> +
> +#else
> +static_assert( !std::indirectly_writable<std::vector<bool>::iterator, bool>
> );
> +static_assert( !std::indirectly_writable<std::vector<bool>::iterator,
> + std::vector<bool>::reference> );
> +#endif
> +
> +int
> +main()
> +{
> + test_swap();
> + test_iter_swap();
> +}
> diff --git
> a/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/ref_swap.cc
> b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/ref_swap.cc
> new file mode 100644
> index 00000000000..2221e3b03f0
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/ref_swap.cc
> @@ -0,0 +1,38 @@
> +// { dg-do run { target c++11 } }
> +
> +#include <vector>
> +#include <testsuite_hooks.h>
> +
> +void
> +test_friend()
> +{
> + std::vector<bool> v{true, false};
> + swap(v[0], v[1]);
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +
> + bool b = true;
> + swap(v[0], b);
> + VERIFY( v[0] == true );
> + VERIFY( b == false );
> +
> + swap(b, v[1]);
> + VERIFY( v[1] == false );
> + VERIFY( b == true );
> +}
> +
> +void
> +test_static()
> +{
> + std::vector<bool> v{true, false};
> + std::vector<bool>::swap(v[0], v[1]); // { dg-warning "deprecated" "::swap"
> { target c++26 } }
> + VERIFY( v[0] == false );
> + VERIFY( v[1] == true );
> +}
> +
> +int
> +main()
> +{
> + test_friend();
> + test_static();
> +}
> diff --git
> a/libstdc++-v3/testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc
>
> b/libstdc++-v3/testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc
> index d2a0218a109..1eb526800f7 100644
> ---
> a/libstdc++-v3/testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc
> +++
> b/libstdc++-v3/testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc
> @@ -53,7 +53,7 @@ constexpr bool
> test_reference_swap()
> {
> std::vector<bool> v1 = {true, false, true};
> - std::vector<bool>::swap(v1[0], v1[1]);
> + std::vector<bool>::swap(v1[0], v1[1]); // { dg-warning "deprecated"
> "::swap" { target c++26 } }
>
> VERIFY(v1[0] == false);
> VERIFY(v1[1] == true);
> --
> 2.54.0
>
