[PATCH 1/2] libstdc++: Implement optional<T&> from P2988R12 [PR121748]
Tomasz Kaminski
tkaminsk@redhat.com
Fri Oct 17 15:20:03 GMT 2025
On Fri, Oct 17, 2025 at 5:18 PM Tomasz Kamiński <tkaminsk@redhat.com> wrote:
> From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
>
> This patch implements optional<T&> based on the P2988R12 paper,
> incorporating
> corrections for LWG4300, LWG4304, and LWG3467. The resolution for LWG4015
> is also extended to cover optional<T&>.
>
> In optional<T> use std::move(__t).operator*() to correctly propagate the
> value
> during move construction from optional<T&>. This is necessary because
> moving
> an optional<T&> must not move the contained object, which is the key
> distinction
> between *std::move(opt) and std::move(*opt).
>
> The implementation deviates from the standard by providing a separate
> std::swap
> overload for std::optional<T&>, which simplifies preserving the resolution
> of
> LWG2766.
>
> This introduces a few changes to make_optional behavior (see included
> test):
> * some previously valid uses of make_optional<T>({...}) (where T is not a
> reference type) now become ill-formed (see
> optional/make_optional_neg.cc).
> * make_optional<T&>(t) and make_optional<const T&>(ct), where decltype(t)
> is T&,
> and decltype(cy) is const T& now produce optional<T&> and
> optional<const T&>
> respectively, instead of optional<T>.
> * a few other uses of make_optional<R> with reference types are now
> ill-formed.
>
> PR libstdc++/121748
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/version.def: Bump value for optional,
> * include/bits/version.h: Regenerate.
> * include/std/optional
> (std::__is_valid_contained_type_for_optional):
> Define.
> (std::optional<T>): Use __is_valid_contained_type_for_optional.
> (optional<T>(const optional<_Up>&), optional<T>(optional<_Up>&&))
> (optional<T>::operator=(const optional<_Up>&))
> (optional<T>::operator=(optional<_Up>&&)): Replace
> std::move(x._M_get())
> with std::move(x).operator*(), and x._M_get() with x.operator*().
> (optional<T>::and_then): Remove uncessary remove_cvref_t.
> (std::optional<T&>): Define new partial specialization.
> (std::swap(std::optional<T&>, std::optional<T&>)): Define.
> (std::make_optional(_Tp&&)): Add non-type template parameter.
> (std::make_optional): Use parenthesis to constructor optional.
> (std::hash<optional<T>>): Add comment.
> * testsuite/20_util/optional/make_optional-2.cc: Guarded not longer
> working example.
> * testsuite/20_util/optional/relops/constrained.cc: Expand test to
> cover optionals of reference.
> * testsuite/20_util/optional/requirements.cc: Ammend for
> optional<T&>.
> * testsuite/20_util/optional/requirements_neg.cc: Likewise.
> * testsuite/20_util/optional/version.cc: Test new value of
> __cpp_lib_optional.
> * testsuite/20_util/optional/make_optional_neg.cc: New test.
> * testsuite/20_util/optional/monadic/ref_neg.cc: New test.
> * testsuite/20_util/optional/ref/access.cc: New test.
> * testsuite/20_util/optional/ref/assign.cc: New test.
> * testsuite/20_util/optional/ref/cons.cc: New test.
> * testsuite/20_util/optional/ref/internal_traits.cc: New test.
> * testsuite/20_util/optional/ref/make_optional/1.cc: New test.
> * testsuite/20_util/optional/ref/make_optional/from_args_neg.cc:
> New test.
> * testsuite/20_util/optional/ref/make_optional/from_lvalue_neg.cc:
> New test.
> * testsuite/20_util/optional/ref/make_optional/from_rvalue_neg.cc:
> New test.
> * testsuite/20_util/optional/ref/monadic.cc: New test.
> * testsuite/20_util/optional/ref/relops.cc: New test.
>
> Co-authored-by: Tomasz Kamiński <tkaminsk@redhat.com>
>
The implementation was provided by Giuseppe, I (Tomasz) have made some
corrections,
and expanded the test cases. The exact split may be found on forge:
https://forge.sourceware.org/gcc/gcc-TEST/pulls/107
> ---
> Tested on x86_64-linux locally. *optional* test also tested with all
> standard modes.
> OK for trunk?
>
> libstdc++-v3/include/bits/version.def | 8 +-
> libstdc++-v3/include/bits/version.h | 7 +-
> libstdc++-v3/include/std/optional | 360 ++++++++++++++-
> .../20_util/optional/make_optional-2.cc | 2 +
> .../20_util/optional/make_optional_neg.cc | 20 +
> .../20_util/optional/monadic/ref_neg.cc | 20 +
> .../testsuite/20_util/optional/ref/access.cc | 119 +++++
> .../testsuite/20_util/optional/ref/assign.cc | 430 ++++++++++++++++++
> .../testsuite/20_util/optional/ref/cons.cc | 356 +++++++++++++++
> .../20_util/optional/ref/internal_traits.cc | 11 +
> .../20_util/optional/ref/make_optional/1.cc | 74 +++
> .../ref/make_optional/from_args_neg.cc | 43 ++
> .../ref/make_optional/from_lvalue_neg.cc | 40 ++
> .../ref/make_optional/from_rvalue_neg.cc | 38 ++
> .../testsuite/20_util/optional/ref/monadic.cc | 192 ++++++++
> .../testsuite/20_util/optional/ref/relops.cc | 229 ++++++++++
> .../20_util/optional/relops/constrained.cc | 86 +++-
> .../20_util/optional/requirements.cc | 6 +-
> .../20_util/optional/requirements_neg.cc | 17 +-
> .../testsuite/20_util/optional/version.cc | 4 +-
> 20 files changed, 2029 insertions(+), 33 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/make_optional_neg.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/monadic/ref_neg.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/optional/ref/access.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/optional/ref/assign.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/optional/ref/cons.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/ref/internal_traits.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/ref/make_optional/1.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_args_neg.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_lvalue_neg.cc
> create mode 100644
> libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_rvalue_neg.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/optional/ref/monadic.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/optional/ref/relops.cc
>
> diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> index 1118da4b541..be15442a50f 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -878,12 +878,16 @@ ftms = {
> // Moved down here (after concepts) by topological sort.
> ftms = {
> name = optional;
> - values = {
> + values = { // optional<T&>
> + v = 202506;
> + cxxmin = 26;
> + };
> + values = { // monadic operations
> v = 202110;
> cxxmin = 23;
> extra_cond = "__glibcxx_concepts";
> };
> - values = {
> + values = { // full constexpr support
> v = 202106;
> cxxmin = 20;
> };
> diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> index c452bbeec8e..e98ecdf94e7 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -985,7 +985,12 @@
> #undef __glibcxx_want_concepts
>
> #if !defined(__cpp_lib_optional)
> -# if (__cplusplus >= 202100L) && (__glibcxx_concepts)
> +# if (__cplusplus > 202302L)
> +# define __glibcxx_optional 202506L
> +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_optional)
> +# define __cpp_lib_optional 202506L
> +# endif
> +# elif (__cplusplus >= 202100L) && (__glibcxx_concepts)
> # define __glibcxx_optional 202110L
> # if defined(__glibcxx_want_all) || defined(__glibcxx_want_optional)
> # define __cpp_lib_optional 202110L
> diff --git a/libstdc++-v3/include/std/optional
> b/libstdc++-v3/include/std/optional
> index e5051d72c82..e6f3a985f50 100644
> --- a/libstdc++-v3/include/std/optional
> +++ b/libstdc++-v3/include/std/optional
> @@ -777,6 +777,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> # define _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL 1
> #endif
>
> + template<typename _Tp>
> + inline constexpr bool __is_valid_contained_type_for_optional =
> + (
> +#if __cpp_lib_optional >= 202506L
> + is_lvalue_reference_v<_Tp> ||
> +#endif
> + (is_object_v<_Tp> && is_destructible_v<_Tp> && !is_array_v<_Tp>)
> + )
> + && !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, nullopt_t>
> + && !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, in_place_t>;
> +
> /**
> * @brief Class template for optional values.
> */
> @@ -795,9 +806,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // Unique tag type.
> optional<_Tp>>
> {
> - static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>);
> - static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
> - static_assert(is_object_v<_Tp> && !is_array_v<_Tp>);
> + static_assert(__is_valid_contained_type_for_optional<_Tp>);
>
> private:
> using _Base = _Optional_base<_Tp>;
> @@ -894,7 +903,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
> {
> if (__t)
> - emplace(__t._M_get());
> + emplace(__t.operator*());
> }
>
> template<typename _Up>
> @@ -906,7 +915,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, _Up>)
> {
> if (__t)
> - emplace(std::move(__t._M_get()));
> + emplace(std::move(__t).operator*());
> }
>
> template<typename... _Args>
> @@ -956,7 +965,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
> {
> if (__t)
> - emplace(__t._M_get());
> + emplace(__t.operator*());
> }
>
> template<typename _Up,
> @@ -969,7 +978,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
> {
> if (__t)
> - emplace(__t._M_get());
> + emplace(__t.operator*());
> }
>
> template<typename _Up,
> @@ -982,7 +991,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, _Up>)
> {
> if (__t)
> - emplace(std::move(__t._M_get()));
> + emplace(std::move(__t).operator*());
> }
>
> template<typename _Up,
> @@ -995,7 +1004,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_constructible_v<_Tp, _Up>)
> {
> if (__t)
> - emplace(std::move(__t._M_get()));
> + emplace(std::move(__t).operator*());
> }
>
> template<typename... _Args,
> @@ -1074,9 +1083,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> if (__u)
> {
> if (this->_M_is_engaged())
> - this->_M_get() = __u._M_get();
> + this->_M_get() = __u.operator*();
> else
> - this->_M_construct(__u._M_get());
> + this->_M_construct(__u.operator*());
> }
> else
> {
> @@ -1108,9 +1117,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> if (__u)
> {
> if (this->_M_is_engaged())
> - this->_M_get() = std::move(__u._M_get());
> + this->_M_get() = std::move(__u).operator*();
> else
> - this->_M_construct(std::move(__u._M_get()));
> + this->_M_construct(std::move(__u).operator*());
> }
> else
> {
> @@ -1310,7 +1319,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> and_then(_Fn&& __f) &
> {
> using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
> - static_assert(__is_optional_v<remove_cvref_t<_Up>>,
> + static_assert(__is_optional_v<_Up>,
> "the function passed to std::optional<T>::and_then
> "
> "must return a std::optional");
> if (has_value())
> @@ -1338,7 +1347,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> and_then(_Fn&& __f) &&
> {
> using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp>>;
> - static_assert(__is_optional_v<remove_cvref_t<_Up>>,
> + static_assert(__is_optional_v<_Up>,
> "the function passed to std::optional<T>::and_then
> "
> "must return a std::optional");
> if (has_value())
> @@ -1352,7 +1361,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> and_then(_Fn&& __f) const &&
> {
> using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp>>;
> - static_assert(__is_optional_v<remove_cvref_t<_Up>>,
> + static_assert(__is_optional_v<_Up>,
> "the function passed to std::optional<T>::and_then
> "
> "must return a std::optional");
> if (has_value())
> @@ -1453,6 +1462,305 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> #endif
> };
>
> +#if __cpp_lib_optional >= 202506L // C++26
> + template<typename _Tp>
> + class optional<_Tp&>
> + {
> + static_assert(__is_valid_contained_type_for_optional<_Tp&>);
> +
> + public:
> + using value_type = _Tp;
> + using iterator = __gnu_cxx::__normal_iterator<_Tp*, optional>;
> +
> + // Constructors.
> + constexpr optional() noexcept = default;
> + constexpr optional(nullopt_t) noexcept : optional() {}
> + constexpr optional(const optional&) noexcept = default;
> +
> + template<typename _Arg>
> + requires is_constructible_v<_Tp&, _Arg>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Arg>)
> + explicit constexpr
> + optional(in_place_t, _Arg&& __arg)
> + {
> + __convert_ref_init_val(std::forward<_Arg>(__arg));
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cvref_t<_Up>, optional>)
> + && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
> + && is_constructible_v<_Tp&, _Up>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
> + explicit(!is_convertible_v<_Up, _Tp&>)
> + constexpr
> + optional(_Up&& __u)
> + noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
> + {
> + __convert_ref_init_val(std::forward<_Up>(__u));
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cvref_t<_Up>, optional>)
> + && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
> + && is_constructible_v<_Tp&, _Up>
> + && reference_constructs_from_temporary_v<_Tp&, _Up>
> + explicit(!is_convertible_v<_Up, _Tp&>)
> + constexpr
> + optional(_Up&& __u) = delete;
> +
> + // optional<U> &
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, _Up&>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Up&>)
> + explicit(!is_convertible_v<_Up&, _Tp&>)
> + constexpr
> + optional(optional<_Up>& __rhs)
> + noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
> + {
> + if (__rhs)
> + __convert_ref_init_val(__rhs.operator*());
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, _Up&>
> + && reference_constructs_from_temporary_v<_Tp&, _Up&>
> + explicit(!is_convertible_v<_Up&, _Tp&>)
> + constexpr
> + optional(optional<_Up>& __rhs) = delete;
> +
> + // const optional<U>&
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, const _Up&>
> + && (!reference_constructs_from_temporary_v<_Tp&, const _Up&>)
> + explicit(!is_convertible_v<const _Up&, _Tp&>)
> + constexpr
> + optional(const optional<_Up>& __rhs)
> + noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
> + {
> + if (__rhs)
> + __convert_ref_init_val(__rhs.operator*());
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, const _Up&>
> + && reference_constructs_from_temporary_v<_Tp&, const _Up&>
> + explicit(!is_convertible_v<const _Up&, _Tp&>)
> + constexpr
> + optional(const optional<_Up>& __rhs) = delete;
> +
> + // optional<U>&&
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, _Up>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
> + explicit(!is_convertible_v<_Up, _Tp&>)
> + constexpr
> + optional(optional<_Up>&& __rhs)
> + noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
> + {
> + if (__rhs)
> + __convert_ref_init_val(std::move(__rhs).operator*());
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, _Up>
> + && reference_constructs_from_temporary_v<_Tp&, _Up>
> + explicit(!is_convertible_v<_Up, _Tp&>)
> + constexpr
> + optional(optional<_Up>&& __rhs) = delete;
> +
> + // const optional<U>&&
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, const _Up>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
> + explicit(!is_convertible_v<const _Up, _Tp&>)
> + constexpr
> + optional(const optional<_Up>&& __rhs)
> + noexcept(is_nothrow_constructible_v<_Tp&, const _Up>)
> + {
> + if (__rhs)
> + __convert_ref_init_val(std::move(__rhs).operator*());
> + }
> +
> + template<typename _Up>
> + requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
> + && (!is_same_v<_Tp&, _Up>)
> + && is_constructible_v<_Tp&, const _Up>
> + && reference_constructs_from_temporary_v<_Tp&, const _Up>
> + explicit(!is_convertible_v<const _Up, _Tp&>)
> + constexpr
> + optional(const optional<_Up>&& __rhs) = delete;
> +
> + constexpr ~optional() = default;
> +
> + // Assignment.
> + constexpr optional& operator=(nullopt_t) noexcept
> + {
> + _M_val = nullptr;
> + return *this;
> + }
> +
> + constexpr optional& operator=(const optional&) noexcept = default;
> +
> + template<typename _Up>
> + requires is_constructible_v<_Tp&, _Up>
> + && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
> + constexpr _Tp&
> + emplace(_Up&& __u)
> + noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
> + {
> + __convert_ref_init_val(std::forward<_Up>(__u));
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 4300. Missing Returns: element in optional<T&>::emplace
> + return *_M_val;
> + }
> +
> + // Swap.
> + constexpr void swap(optional& __rhs) noexcept
> + { std::swap(_M_val, __rhs._M_val); }
> +
> + // Iterator support.
> + constexpr iterator begin() const noexcept
> + {
> + return iterator(_M_val);
> + }
> +
> + constexpr iterator end() const noexcept
> + {
> + return begin() + has_value();
> + }
> +
> + // Observers.
> + constexpr _Tp* operator->() const noexcept
> + {
> + __glibcxx_assert(_M_val); // hardened precondition
> + return _M_val;
> + }
> +
> + constexpr _Tp& operator*() const noexcept
> + {
> + __glibcxx_assert(_M_val); // hardened precondition
> + return *_M_val;
> + }
> +
> + constexpr explicit operator bool() const noexcept
> + {
> + return _M_val;
> + }
> +
> + constexpr bool has_value() const noexcept
> + {
> + return _M_val;
> + }
> +
> + constexpr _Tp& value() const
> + {
> + if (_M_val)
> + return *_M_val;
> + __throw_bad_optional_access();
> + }
> +
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 4304. std::optional<NonReturnable&> is ill-formed due to value_or
> + template<typename _Up = remove_cv_t<_Tp>>
> + requires is_object_v<_Tp> && (!is_array_v<_Tp>)
> + constexpr decay_t<_Tp>
> + value_or(_Up&& __u) const
> + {
> + using _Xp = remove_cv_t<_Tp>;
> + static_assert(is_constructible_v<_Xp, _Tp&>);
> + static_assert(is_convertible_v<_Up, _Xp>);
> + return _M_val ? *_M_val :
> static_cast<_Xp>(std::forward<_Up>(__u));
> + }
> +
> + // Monadic operations.
> + template<typename _Fn>
> + constexpr auto
> + and_then(_Fn&& __f) const
> + {
> + using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
> + static_assert(__is_optional_v<_Up>,
> + "the function passed to
> std::optional<T&>::and_then "
> + "must return a std::optional");
> + if (has_value())
> + return std::__invoke(std::forward<_Fn>(__f), *_M_val);
> + else
> + return _Up();
> + }
> +
> + template<typename _Fn>
> + constexpr
> + optional<remove_cv_t<invoke_result_t<_Fn, _Tp&>>>
> + transform(_Fn&& __f) const
> + {
> + using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
> + if (has_value())
> + return optional<_Up>(_Optional_func<_Fn>{__f}, *_M_val);
> + else
> + return optional<_Up>();
> + }
> +
> + template<typename _Fn>
> + requires invocable<_Fn>
> + constexpr
> + optional
> + or_else(_Fn&& __f) const
> + {
> + static_assert(is_same_v<remove_cvref_t<invoke_result_t<_Fn>>,
> optional>,
> + "the function passed to std::optional<T&>::or_else
> "
> + "must return a std::optional<T&>");
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 4367. Improve optional<T&>::or_else
> + if (has_value())
> + return *this;
> + else
> + return std::forward<_Fn>(__f)();
> + }
> +
> + // Modifiers.
> + constexpr void reset() noexcept
> + {
> + _M_val = nullptr;
> + }
> +
> + private:
> + _Tp *_M_val = nullptr;
> +
> + template<typename _Up> friend class optional;
> +
> + template<typename _Up>
> + constexpr
> + void
> + __convert_ref_init_val(_Up&& __u)
> + noexcept
> + {
> + _Tp& __r(std::forward<_Up>(__u));
> + _M_val = std::addressof(__r);
> + }
> +
> + template<typename _Fn, typename _Value>
> + explicit constexpr
> + optional(_Optional_func<_Fn> __f, _Value&& __v)
> + {
> + _Tp& __r = std::__invoke(std::forward<_Fn>(__f._M_f),
> std::forward<_Value>(__v));
> + _M_val = std::addressof(__r);
> + }
> + };
> +#endif // __cpp_lib_optional >= 202506L
> +
> template<typename _Tp>
> using __optional_relop_t =
> enable_if_t<is_convertible_v<_Tp, bool>, bool>;
> @@ -1740,19 +2048,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(noexcept(__lhs.swap(__rhs)))
> { __lhs.swap(__rhs); }
>
> +#if __cpp_lib_optional >= 202506L
> + // We deviate from standard, that do not declared separate swap overload
> + // from optional<T&>.
> + template<typename _Tp>
> + constexpr void
> + swap(optional<_Tp&>& __lhs, optional<_Tp&>& __rhs) noexcept
> + { __lhs.swap(__rhs); }
> +#endif
> +
> // _GLIBCXX_RESOLVE_LIB_DEFECTS
> // 2766. Swapping non-swappable types
> template<typename _Tp>
> enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
> swap(optional<_Tp>&, optional<_Tp>&) = delete;
>
> +#if __cpp_lib_optional >= 202506L
> + template<int = 0, typename _Tp>
> +#else
> template<typename _Tp>
> +#endif
> constexpr
> enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
> optional<decay_t<_Tp>>>
> make_optional(_Tp&& __t)
> noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
> - { return optional<decay_t<_Tp>>{ std::forward<_Tp>(__t) }; }
> + { return optional<decay_t<_Tp>>( std::forward<_Tp>(__t) ); }
>
> template<typename _Tp, typename... _Args>
> constexpr
> @@ -1760,7 +2081,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> optional<_Tp>>
> make_optional(_Args&&... __args)
> noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
> - { return optional<_Tp>{ in_place, std::forward<_Args>(__args)... }; }
> + { return optional<_Tp>( in_place, std::forward<_Args>(__args)... ); }
>
> template<typename _Tp, typename _Up, typename... _Args>
> constexpr
> @@ -1768,7 +2089,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> optional<_Tp>>
> make_optional(initializer_list<_Up> __il, _Args&&... __args)
> noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
> _Args...>)
> - { return optional<_Tp>{ in_place, __il,
> std::forward<_Args>(__args)... }; }
> + { return optional<_Tp>( in_place, __il,
> std::forward<_Args>(__args)... ); }
>
> // Hash.
>
> @@ -1796,6 +2117,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> template<typename _Tp>
> struct hash<optional<_Tp>>
> + // hash for optional<T&> is disabled because is_hash_enabled_for<T&>
> is false
> : public __conditional_t<__is_hash_enabled_for<remove_const_t<_Tp>>,
> __optional_hash<_Tp>,
> __hash_not_enabled<_Tp>>
> diff --git a/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
> b/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
> index f383b519c89..0aa2ac5ed93 100644
> --- a/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
> +++ b/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
> @@ -70,7 +70,9 @@ static_assert( can_make_optional2<int, int&>::value );
> static_assert( noexcept(std::make_optional(i)) );
> static_assert( ! can_make_optional2<void, void>::value );
> static_assert( can_make_optional2<Cont, Cont>::value );
> +#if __cplusplus <= 202302
> static_assert( noexcept(std::make_optional<Cont>({})) );
> +#endif
> static_assert( can_make_optional2<Cont, const Cont&>::value );
> static_assert( ! noexcept(std::make_optional(c)) );
> static_assert( can_make_optional2<Cont, int>::value );
> diff --git a/libstdc++-v3/testsuite/20_util/optional/make_optional_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/make_optional_neg.cc
> new file mode 100644
> index 00000000000..09499477233
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/make_optional_neg.cc
> @@ -0,0 +1,20 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <initializer_list>
> +#include <optional>
> +
> +struct S { int x; int* p; };
> +int v;
> +
> +auto os1 = std::make_optional<S>({1, &v}); // { dg-error "no matching
> function for" "" { target c++26 } }
> +
> +struct Cont
> +{
> + Cont();
> + Cont(std::initializer_list<int>, int);
> +};
> +
> +auto oc1 = std::make_optional<Cont>({}); // { dg-error "no matching
> function for" "" { target c++26 } }
> +
> +// { dg-prune-output "no type named 'type' in 'struct std::enable_if" }
> +// { dg-prune-output "type/value mismatch at argument 1 in template
> parameter list" }
> diff --git a/libstdc++-v3/testsuite/20_util/optional/monadic/ref_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/monadic/ref_neg.cc
> new file mode 100644
> index 00000000000..ed1b42b1992
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/monadic/ref_neg.cc
> @@ -0,0 +1,20 @@
> +// { dg-do compile { target c++23 } }
> +
> +#include <optional>
> +
> +struct S { int x; int y; };
> +
> +void test()
> +{
> + std::optional<S> o;
> + const std::optional<S>& co = o;
> +
> + o.transform(&S::x); // { dg-error "from here" "optional<int&>" {
> target c++23_down } }
> + co.transform(&S::x); // { dg-error "from here" "optional<const int&>" {
> target c++23_down } }
> + std::move(o).transform(&S::x); // { dg-error "from here"
> "optional<int&&>" }
> + std::move(co).transform(&S::x); // { dg-error "from here"
> "optional<const int&&>" }
> +}
> +
> +// { dg-prune-output "in a union may not have reference type" }
> +// { dg-prune-output "static assertion failed" }
> +// { dg-prune-output "forming pointer to reference type" }
> diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
> new file mode 100644
> index 00000000000..37c8ff355a6
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/access.cc
> @@ -0,0 +1,119 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <optional>
> +#include <type_traits>
> +#include <testsuite_hooks.h>
> +
> +struct NonMovable
> +{
> + constexpr NonMovable() {}
> + NonMovable(NonMovable&&) = delete;
> +};
> +
> +template<typename T>
> +constexpr
> +void test_value(T& t)
> +{
> + std::optional<T&> o1(t);
> + const std::optional<T&> co1(t);
> +
> + static_assert( std::is_same_v<decltype(o1.value()), T&> );
> + VERIFY( &o1.value() == &t );
> +
> + static_assert( std::is_same_v<decltype(co1.value()), T&> );
> + VERIFY( &co1.value() == &t );
> +
> + static_assert( std::is_same_v<decltype(std::move(o1).value()), T&> );
> + VERIFY( &std::move(o1).value() == &t );
> +
> + static_assert( std::is_same_v<decltype(std::move(co1).value()), T&> );
> + VERIFY( &std::move(co1).value() == &t );
> +
> + std::optional<const T&> o2(t);
> + static_assert( std::is_same_v<decltype(o2.value()), const T&> );
> + VERIFY( &o2.value() == &t );
> +}
> +
> +struct Tracker
> +{
> + int copy = 0;
> + int move = 0;
> +
> + constexpr Tracker(int v) : copy(v), move(v) {}
> +
> + constexpr Tracker(Tracker const& o)
> + : copy(o.copy+1), move(o.move)
> + {}
> +
> + constexpr Tracker(Tracker&& o)
> + : copy(o.copy), move(o.move+1)
> + {}
> +
> + Tracker& operator=(Tracker) = delete;
> +};
> +
> +constexpr
> +void test_value_or()
> +{
> + Tracker t(100), u(200);
> + std::optional<Tracker&> o(t);
> +
> + Tracker r1 = o.value_or(u);
> + VERIFY( r1.copy == 101 );
> + VERIFY( r1.move == 100 );
> + Tracker r2 = o.value_or(std::move(u));
> + VERIFY( r2.copy == 101 );
> + VERIFY( r2.move == 100 );
> + Tracker r3 = std::move(o).value_or(u);
> + VERIFY( r3.copy == 101 );
> + VERIFY( r3.move == 100 );
> + Tracker r4 = std::move(o).value_or(std::move(u));
> + VERIFY( r4.copy == 101 );
> + VERIFY( r4.move == 100 );
> +
> + o.reset();
> + Tracker r5 = o.value_or(u);
> + VERIFY( r5.copy == 201 );
> + VERIFY( r5.move == 200 );
> + Tracker r6 = o.value_or(std::move(u));
> + VERIFY( r6.copy == 200 );
> + VERIFY( r6.move == 201 );
> + Tracker r7 = std::move(o).value_or(u);
> + VERIFY( r7.copy == 201 );
> + VERIFY( r7.move == 200 );
> + Tracker r8 = std::move(o).value_or(std::move(u));
> + VERIFY( r8.copy == 200 );
> + VERIFY( r8.move == 201 );
> +}
> +
> +template<typename T>
> +concept has_value_or_for = requires(std::optional<T&> t, T& u)
> +{ t.value_or(u); };
> +
> +static_assert( has_value_or_for<int> );
> +static_assert( has_value_or_for<NonMovable> );
> +static_assert( !has_value_or_for<int[2]> );
> +static_assert( has_value_or_for<int(*)[2]> );
> +static_assert( !has_value_or_for<int()> );
> +static_assert( has_value_or_for<int(*)()> );
> +
> +int i;
> +NonMovable nm;
> +int arr[2];
> +int foo();
> +
> +int main()
> +{
> + auto test_all = [] {
> + test_value<int>(i);
> + test_value<NonMovable>(nm);
> + test_value<int[2]>(arr);
> + test_value<int()>(foo);
> +
> + test_value_or();
> + return true;
> + };
> +
> + test_all();
> + static_assert(test_all());
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/assign.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/assign.cc
> new file mode 100644
> index 00000000000..be8b1c84eca
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/assign.cc
> @@ -0,0 +1,430 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <optional>
> +#include <type_traits>
> +#include <testsuite_hooks.h>
> +
> +struct NonTrivial
> +{
> + constexpr NonTrivial() {}
> + constexpr NonTrivial(NonTrivial const&) {};
> + constexpr ~NonTrivial() {};
> +};
> +
> +struct NonMovable
> +{
> + NonMovable() = default;
> + NonMovable(NonMovable&&) = delete;
> +};
> +
> +template<typename T>
> +struct Conv
> +{
> + T t;
> +
> + constexpr operator T() const noexcept
> + { return t; }
> +};
> +
> +struct Tracker
> +{
> + struct Counter
> + {
> + int copy;
> + int move;
> + };
> +
> + Counter ctor{0,0};
> + Counter assign{0,0};
> +
> + Tracker() = default;
> +
> + constexpr Tracker(Tracker const& o)
> + : ctor(o.ctor), assign(o.assign)
> + {
> + ctor.copy += 1;
> + }
> +
> + constexpr Tracker(Tracker&& o)
> + : ctor(o.ctor), assign(o.assign)
> + {
> + ctor.move += 1;
> + }
> +
> + constexpr Tracker& operator=(const Tracker& o)
> + {
> + assign.copy += 1;
> + return *this;
> + }
> +
> + constexpr Tracker& operator=(Tracker&& o)
> + {
> + assign.move += 1;
> + return *this;
> + }
> +
> +};
> +
> +template<typename T>
> +void
> +test_trivial()
> +{
> + static_assert(std::is_copy_assignable_v<std::optional<T&>>);
> + static_assert(std::is_move_assignable_v<std::optional<T&>>);
> +}
> +
> +constexpr void
> +test_trivial_all()
> +{
> + test_trivial<int>();
> + test_trivial<NonTrivial>();
> + test_trivial<std::optional<int&>>();
> +}
> +
> +constexpr void
> +test_copy()
> +{
> + Tracker t, u;
> + std::optional<Tracker&> e;
> + std::optional<Tracker&> o1(t);
> + std::optional<Tracker&> o2(u);
> +
> + o2 = o1;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &t );
> + VERIFY( t.ctor.copy == 0 );
> + VERIFY( t.ctor.move == 0 );
> + VERIFY( t.assign.copy == 0 );
> + VERIFY( t.assign.move == 0 );
> +
> + o2 = e;
> + VERIFY( !o2.has_value() );
> +
> + o2 = std::move(o1);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &t );
> + VERIFY( t.ctor.copy == 0 );
> + VERIFY( t.ctor.move == 0 );
> + VERIFY( t.assign.copy == 0 );
> + VERIFY( t.assign.move == 0 );
> +
> + o2 = std::move(e);
> + VERIFY( !o2.has_value() );
> +}
> +
> +template<typename T, typename U>
> +concept can_emplace = requires (T t, U&& u)
> +{ t.emplace(std::forward<U>(u)); };
> +
> +constexpr void
> +test_from_value()
> +{
> + NonTrivial v, u;
> + const NonTrivial& cv = v;
> + const std::optional<NonTrivial&> s(u);
> + std::optional<NonTrivial&> o1;
> + std::optional<const NonTrivial&> co1;
> +
> + o1 = s;
> + o1 = v;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> +
> + o1.reset();
> + VERIFY( !o1.has_value() );
> +
> + o1 = v;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const NonTrivial&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + NonTrivial> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const NonTrivial> );
> +
> + o1 = s;
> + o1.emplace(v);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> +
> + o1 = std::nullopt;
> + VERIFY( !o1.has_value() );
> +
> + o1.emplace(v);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> +
> + static_assert( !can_emplace<std::optional<NonTrivial&>, const
> NonTrivial&> );
> + static_assert( !can_emplace<std::optional<NonTrivial&>, NonTrivial> );
> + static_assert( !can_emplace<std::optional<NonTrivial&>, const
> NonTrivial> );
> +
> + co1 = s;
> + co1 = v;
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v );
> +
> + co1 = std::nullopt;
> + co1 = cv;
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v );
> + // No binding to rvalue
> + static_assert( !std::is_assignable_v<std::optional<const NonTrivial&>,
> + NonTrivial> );
> + static_assert( !std::is_assignable_v<std::optional<const NonTrivial&>,
> + const NonTrivial> );
> +
> + co1 = std::nullopt;
> + co1.emplace(v);
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v );
> +
> + co1 = s;
> + co1.emplace(cv);
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v );
> + // No binding to rvalue
> + static_assert( !can_emplace<std::optional<const NonTrivial&>, const
> NonTrivial> );
> + static_assert( !can_emplace<std::optional<const NonTrivial&>,
> NonTrivial> );
> +
> +
> + // Conversion create a pr-value that would bind to temporary
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + Conv<NonTrivial>&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const Conv<NonTrivial>&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + Conv<NonTrivial>> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const Conv<NonTrivial>> );
> +
> + static_assert( !can_emplace<std::optional<NonTrivial&>,
> Conv<NonTrivial>&> );
> + static_assert( !can_emplace<std::optional<NonTrivial&>, const
> Conv<NonTrivial>&> );
> + static_assert( !can_emplace<std::optional<NonTrivial&>,
> Conv<NonTrivial>> );
> + static_assert( !can_emplace<std::optional<NonTrivial&>, const
> Conv<NonTrivial>> );
> +
> + Conv<NonTrivial&> rw(v);
> + const Conv<NonTrivial&> crw(v);
> +
> + o1 = std::nullopt;
> + o1 = rw;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = s;
> + o1 = crw;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = s;
> + o1 = std::move(rw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = std::nullopt;
> + o1 = std::move(crw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> +
> + o1 = s;
> + o1.emplace(rw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = std::nullopt;
> + o1.emplace(crw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = std::nullopt;
> + o1.emplace(std::move(rw));
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + o1 = s;
> + o1.emplace(std::move(crw));
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> +}
> +
> +constexpr void
> +test_from_opt_value()
> +{
> + NonTrivial u;
> + std::optional<NonTrivial> v(std::in_place);
> + const std::optional<NonTrivial>& cv = v;
> +
> + const std::optional<NonTrivial&> s(u);
> + std::optional<NonTrivial&> o1;
> + std::optional<const NonTrivial&> co1;
> +
> + o1 = s;
> + o1 = v;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + o1 = std::nullopt;
> + o1 = v;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const std::optional<NonTrivial>&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + std::optional<NonTrivial>> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const std::optional<NonTrivial>> );
> +
> + co1 = s;
> + co1 = v;
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v.value() );
> + co1 = std::nullopt;
> + co1 = cv;
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v.value() );
> + // No binding to rvalue
> + static_assert( !std::is_assignable_v<std::optional<const NonTrivial&>,
> + std::optional<NonTrivial>> );
> + static_assert( !std::is_assignable_v<std::optional<const NonTrivial&>,
> + const std::optional<NonTrivial>> );
> +
> + // Conversion create a pr-value that would bind to temporary
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + std::optional<Conv<NonTrivial>>&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const
> std::optional<Conv<NonTrivial>>&> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + std::optional<Conv<NonTrivial>>> );
> + static_assert( !std::is_assignable_v<std::optional<NonTrivial&>,
> + const
> std::optional<Conv<NonTrivial>>> );
> +
> + std::optional<Conv<NonTrivial&>> rw(*v);
> + std::optional<const Conv<NonTrivial&>> crw(*v);
> +
> + o1 = std::nullopt;
> + o1 = rw;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + o1 = s;
> + o1 = crw;
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + o1 = s;
> + o1 = std::move(rw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + o1 = std::nullopt;
> + o1 = std::move(crw);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> +}
> +
> +constexpr void
> +test_to_opt_value()
> +{
> + Tracker t;
> + std::optional<Tracker&> er;
> + std::optional<Tracker&> r(t);
> + const std::optional<Tracker&> cr(t);
> +
> + std::optional<Tracker> o1;
> + o1 = r;
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 0 );
> + VERIFY( o1->assign.move == 0 );
> +
> + o1 = r;
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 1 );
> + VERIFY( o1->assign.move == 0 );
> +
> + o1 = er;
> + VERIFY( !o1.has_value() );
> +
> + o1 = cr;
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 0 );
> + VERIFY( o1->assign.move == 0 );
> +
> + o1 = cr;
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 1 );
> + VERIFY( o1->assign.move == 0 );
> +
> + o1 = std::move(er);
> +
> + o1 = std::move(r);
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 0 );
> + VERIFY( o1->assign.move == 0 );
> +
> + o1 = std::move(cr);
> + VERIFY( o1.has_value() );
> + VERIFY( o1->ctor.copy == 1 );
> + VERIFY( o1->ctor.move == 0 );
> + VERIFY( o1->assign.copy == 1 );
> + VERIFY( o1->assign.move == 0 );
> +}
> +
> +constexpr void
> +test_swap()
> +{
> + NonMovable a, b;
> + std::optional<NonMovable&> oa(a), ob(b);
> +
> + oa.swap(ob);
> + static_assert(noexcept(oa.swap(ob)));
> + VERIFY( oa.has_value() );
> + VERIFY( &oa.value() == &b );
> + VERIFY( ob.has_value() );
> + VERIFY( &ob.value() == &a );
> +
> + swap(oa, ob);
> + static_assert(std::is_nothrow_swappable_v<std::optional<NonMovable&>>);
> + VERIFY( oa.has_value() );
> + VERIFY( &oa.value() == &a );
> + VERIFY( ob.has_value() );
> + VERIFY( &ob.value() == &b );
> +
> + ob.reset();
> + oa.swap(ob);
> + VERIFY( !oa.has_value() );
> + VERIFY( ob.has_value() );
> + VERIFY( &ob.value() == &a );
> +
> + ob.reset();
> + std::swap(oa, ob);
> + VERIFY( !oa.has_value() );
> + VERIFY( !ob.has_value() );
> +
> + std::optional<const NonMovable&> ca(a), cb(b);
> + swap(ca, cb);
> + VERIFY( ca.has_value() );
> + VERIFY( &ca.value() == &b );
> + VERIFY( cb.has_value() );
> + VERIFY( &cb.value() == &a );
> +
> + static_assert(!std::is_swappable_with_v<std::optional<int>&,
> std::optional<int&>&>);
> +}
> +
> +int main()
> +{
> + auto test_all = [] {
> + test_copy();
> + test_from_value();
> + test_from_opt_value();
> + test_to_opt_value();
> + test_swap();
> + return true;
> + };
> +
> + test_all();
> + static_assert(test_all());
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/cons.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/cons.cc
> new file mode 100644
> index 00000000000..b13e8b92329
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/cons.cc
> @@ -0,0 +1,356 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <optional>
> +#include <type_traits>
> +#include <testsuite_hooks.h>
> +
> +struct NonTrivial
> +{
> + constexpr NonTrivial() {}
> + constexpr NonTrivial(NonTrivial const&) {};
> + constexpr ~NonTrivial() {};
> +};
> +
> +struct NonMovable
> +{
> + constexpr NonMovable() {}
> + NonMovable(NonMovable&&) = delete;
> +};
> +
> +template<typename T>
> +struct Conv
> +{
> + T t;
> +
> + constexpr operator T() const noexcept
> + { return t; }
> +};
> +
> +struct Tracker
> +{
> + int copy = 0;
> + int move = 0;
> +
> + Tracker() = default;
> +
> + constexpr Tracker(Tracker const& o)
> + : copy(o.copy+1), move(o.move)
> + {}
> +
> + constexpr Tracker(Tracker&& o)
> + : copy(o.copy), move(o.move+1)
> + {}
> +
> + Tracker& operator=(Tracker) = delete;
> +};
> +
> +template<typename T>
> +void
> +test_trivial()
> +{
> + static_assert(std::is_trivially_copyable_v<std::optional<T&>>);
> + static_assert(std::is_copy_constructible_v<std::optional<T&>>);
> + static_assert(std::is_move_constructible_v<std::optional<T&>>);
> + static_assert(std::is_destructible_v<std::optional<T&>>);
> +}
> +
> +constexpr void
> +test_trivial_all()
> +{
> + test_trivial<int>();
> + test_trivial<NonTrivial>();
> + test_trivial<NonMovable>();
> + test_trivial<std::optional<int&>>();
> +}
> +
> +constexpr void
> +test_copy()
> +{
> + Tracker t;
> + std::optional<Tracker&> o1(t);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> + VERIFY( t.copy == 0 );
> + VERIFY( t.move == 0 );
> +
> + std::optional<Tracker&> o2(o1);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &t );
> + VERIFY( t.copy == 0 );
> + VERIFY( t.move == 0 );
> +
> + std::optional<Tracker&> o3(std::move(o1));
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> + VERIFY( o3.has_value() );
> + VERIFY( &o3.value() == &t );
> + VERIFY( t.copy == 0 );
> + VERIFY( t.move == 0 );
> +
> + std::optional<Tracker&> e;
> + VERIFY( !e.has_value() );
> +
> + std::optional<Tracker&> o4(e);
> + VERIFY( !e.has_value() );
> + VERIFY( !o4.has_value() );
> +
> + std::optional<Tracker&> o5(std::move(e));
> + VERIFY( !e.has_value() );
> + VERIFY( !o5.has_value() );
> +}
> +
> +
> +constexpr void
> +test_from_value()
> +{
> + NonTrivial v;
> + const NonTrivial& cv = v;
> +
> + std::optional<NonTrivial&> o1(v);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const NonTrivial&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + NonTrivial> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const NonTrivial> );
> +
> + std::optional<NonTrivial&> o2(std::in_place, v);
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &v );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t, const
> NonTrivial&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t, NonTrivial> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t, const
> NonTrivial> );
> +
> + std::optional<const NonTrivial&> co1(v);
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v );
> + std::optional<const NonTrivial&> co2(cv);
> + VERIFY( co2.has_value() );
> + VERIFY( &co2.value() == &v );
> + // No binding to rvalue
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + NonTrivial> );
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + const NonTrivial> );
> +
> + std::optional<const NonTrivial&> co3(std::in_place, v);
> + VERIFY( co3.has_value() );
> + VERIFY( &co3.value() == &v );
> + std::optional<const NonTrivial&> co4(std::in_place, cv);
> + VERIFY( co4.has_value() );
> + VERIFY( &co4.value() == &v );
> + // No binding to rvalue
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + std::in_place_t, NonTrivial> );
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + std::in_place_t, const
> NonTrivial> );
> +
> + // Conversion create a pr-value that would bind to temporary
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + Conv<NonTrivial>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const Conv<NonTrivial>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + Conv<NonTrivial>> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const Conv<NonTrivial>> );
> +
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t,
> Conv<NonTrivial>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t, const
> Conv<NonTrivial>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t,
> Conv<NonTrivial>> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::in_place_t, const
> Conv<NonTrivial>> );
> +
> + Conv<NonTrivial&> rw(v);
> + const Conv<NonTrivial&> crw(v);
> +
> + std::optional<NonTrivial&> ro1(rw);
> + VERIFY( ro1.has_value() );
> + VERIFY( &ro1.value() == &v );
> + std::optional<NonTrivial&> ro2(crw);
> + VERIFY( ro2.has_value() );
> + VERIFY( &ro2.value() == &v );
> + std::optional<NonTrivial&> ro3(std::move(rw));
> + VERIFY( ro3.has_value() );
> + VERIFY( &ro3.value() == &v );
> + std::optional<NonTrivial&> ro4(std::move(crw));
> + VERIFY( ro4.has_value() );
> + VERIFY( &ro4.value() == &v );
> +
> + std::optional<NonTrivial&> ro5(std::in_place, rw);
> + VERIFY( ro5.has_value() );
> + VERIFY( &ro5.value() == &v );
> + std::optional<NonTrivial&> ro6(std::in_place, crw);
> + VERIFY( ro6.has_value() );
> + VERIFY( &ro6.value() == &v );
> + std::optional<NonTrivial&> ro7(std::in_place, std::move(rw));
> + VERIFY( ro7.has_value() );
> + VERIFY( &ro7.value() == &v );
> + std::optional<NonTrivial&> ro8(std::in_place, std::move(crw));
> + VERIFY( ro8.has_value() );
> + VERIFY( &ro8.value() == &v );
> +}
> +
> +constexpr void
> +test_from_opt_value()
> +{
> + std::optional<NonTrivial> v(std::in_place);
> + const std::optional<NonTrivial>& cv = v;
> +
> + std::optional<NonTrivial&> o1(v);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &v.value() );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const
> std::optional<NonTrivial>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::optional<NonTrivial>> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const std::optional<NonTrivial>>
> );
> +
> + std::optional<const NonTrivial&> co1(v);
> + VERIFY( co1.has_value() );
> + VERIFY( &co1.value() == &v.value() );
> + std::optional<const NonTrivial&> co2(cv);
> + VERIFY( co2.has_value() );
> + VERIFY( &co2.value() == &v.value() );
> + // No binding to rvalue
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + std::optional<NonTrivial>> );
> + static_assert( !std::is_constructible_v<std::optional<const
> NonTrivial&>,
> + const std::optional<NonTrivial>>
> );
> +
> + // Conversion create a pr-value that would bind to temporary
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> +
> std::optional<Conv<NonTrivial>>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const
> std::optional<Conv<NonTrivial>>&> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + std::optional<Conv<NonTrivial>>>
> );
> + static_assert( !std::is_constructible_v<std::optional<NonTrivial&>,
> + const
> std::optional<Conv<NonTrivial>>> );
> +
> + std::optional<Conv<NonTrivial&>> rw(*v);
> + std::optional<const Conv<NonTrivial&>> crw(*v);
> +
> + std::optional<NonTrivial&> ro1(rw);
> + VERIFY( ro1.has_value() );
> + VERIFY( &ro1.value() == &v.value() );
> + std::optional<NonTrivial&> ro2(crw);
> + VERIFY( ro2.has_value() );
> + VERIFY( &ro2.value() == &v.value() );
> + std::optional<NonTrivial&> ro3(std::move(rw));
> + VERIFY( ro3.has_value() );
> + VERIFY( &ro3.value() == &v.value() );
> + std::optional<NonTrivial&> ro4(std::move(crw));
> + VERIFY( ro4.has_value() );
> + VERIFY( &ro4.value() == &v.value() );
> +}
> +
> +constexpr void
> +test_to_opt_value()
> +{
> + Tracker t;
> + std::optional<Tracker&> r(t);
> + const std::optional<Tracker&> cr(t);
> +
> + std::optional<Tracker> o1(r);
> + VERIFY( o1.has_value() );
> + VERIFY( o1->copy == 1 );
> + VERIFY( o1->move == 0 );
> +
> + std::optional<Tracker> o2(cr);
> + VERIFY( o2.has_value() );
> + VERIFY( o2->copy == 1 );
> + VERIFY( o2->move == 0 );
> +
> + std::optional<Tracker> o3(std::move(r));
> + VERIFY( o3.has_value() );
> + VERIFY( o3->copy == 1 );
> + VERIFY( o3->move == 0 );
> +
> + std::optional<Tracker> o4(std::move(cr));
> + VERIFY( o4.has_value() );
> + VERIFY( o4->copy == 1 );
> + VERIFY( o4->move == 0 );
> +
> + std::optional<Tracker&> er;
> + const std::optional<Tracker&> cer;
> +
> + std::optional<Tracker> e1(er);
> + VERIFY( !e1.has_value() );
> +
> + std::optional<Tracker> e2(cer);
> + VERIFY( !e2.has_value() );
> +
> + std::optional<Tracker> e3(std::move(er));
> + VERIFY( !e3.has_value() );
> +
> + std::optional<Tracker> e4(std::move(cer));
> + VERIFY( !e4.has_value() );
> +}
> +
> +constexpr void
> +test_opt_opt()
> +{
> + std::optional<int> s(43);
> +
> + std::optional<std::optional<int>&> o1(s);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &s );
> +
> + std::optional<std::optional<int>&> o2(std::in_place, s);
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &s );
> +
> + std::optional<std::optional<int>> o3(o1);
> + VERIFY( o2.has_value() );
> + VERIFY( o2.value().has_value() );
> + VERIFY( o2.value() == 43 );
> +
> + s.reset();
> + std::optional<std::optional<int>&> o4(s);
> + VERIFY( o4.has_value() );
> + VERIFY( &o4.value() == &s );
> +
> + std::optional<std::optional<int>&> o5(std::in_place, s);
> + VERIFY( o5.has_value() );
> + VERIFY( &o5.value() == &s );
> +
> + std::optional<std::optional<int>> o6(o1);
> + VERIFY( o6.has_value() );
> + VERIFY( !o6.value().has_value() );
> +
> + std::optional<std::optional<int>> s2(std::in_place);
> + std::optional<std::optional<int>&> oo1(s2);
> + VERIFY( oo1.has_value() );
> + VERIFY( &oo1.value() == &s2.value() );
> +
> + s2.reset();
> + std::optional<std::optional<int>&> oo2(s2);
> + VERIFY( !oo2.has_value() );
> +}
> +
> +int main()
> +{
> + auto test_all = [] {
> + test_copy();
> + test_from_value();
> + test_from_opt_value();
> + test_to_opt_value();
> + test_opt_opt();
> + return true;
> + };
> +
> + test_all();
> + static_assert(test_all());
> +}
> diff --git
> a/libstdc++-v3/testsuite/20_util/optional/ref/internal_traits.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/internal_traits.cc
> new file mode 100644
> index 00000000000..ef50da7e9fa
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/internal_traits.cc
> @@ -0,0 +1,11 @@
> +// { dg-do compile { target c++26 } }
> +
> +#include <optional>
> +#include <variant>
> +
> +template<typename T>
> +constexpr bool _Never_valueless
> + = std::__detail::__variant::_Never_valueless_alt<T>::value;
> +
> +static_assert( _Never_valueless<std::optional<int&>> );
> +static_assert( _Never_valueless<std::optional<const int&>> );
> diff --git
> a/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/1.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/1.cc
> new file mode 100644
> index 00000000000..d9946d034ef
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/1.cc
> @@ -0,0 +1,74 @@
> +// { dg-do run { target c++20 } }
> +
> +#include <optional>
> +#include <utility>
> +#include <testsuite_hooks.h>
> +
> +struct NonTrivial
> +{
> + constexpr NonTrivial() {}
> + constexpr NonTrivial(NonTrivial const&) {};
> + constexpr ~NonTrivial() {};
> +};
> +
> +template<typename T>
> +struct Conv
> +{
> + T t;
> +
> + constexpr operator T() const noexcept
> + { return t; }
> +};
> +
> +constexpr bool test()
> +{
> + NonTrivial t;
> + const NonTrivial& ct = t;
> +
> +#if __cplusplus > 202302
> + auto o1 = std::make_optional<NonTrivial&>(t);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() == &t );
> +
> + auto o2 = std::make_optional<const NonTrivial&>(t);
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() == &t );
> +
> + auto o3 = std::make_optional<const NonTrivial&>(ct);
> + VERIFY( o3.has_value() );
> + VERIFY( &o3.value() == &t );
> +
> + Conv<NonTrivial&> rw(t);
> + auto o4 = std::make_optional<NonTrivial&>(rw);
> + VERIFY( o4.has_value() );
> + VERIFY( &o4.value() == &t );
> +
> + auto o5 = std::make_optional<NonTrivial&>(std::as_const(rw));
> + VERIFY( o5.has_value() );
> + VERIFY( &o5.value() == &t );
> +
> + auto o6 = std::make_optional<NonTrivial&>(Conv<NonTrivial&>(t));
> + VERIFY( o6.has_value() );
> + VERIFY( &o6.value() == &t );
> +#else
> + auto o1 = std::make_optional<NonTrivial&>(t);
> + VERIFY( o1.has_value() );
> + VERIFY( &o1.value() != &t );
> +
> + auto o3 = std::make_optional<const NonTrivial&>(ct);
> + VERIFY( o3.has_value() );
> + VERIFY( &o3.value() != &t );
> +
> + auto o2 = std::make_optional<NonTrivial&&>(std::move(t));
> + VERIFY( o2.has_value() );
> + VERIFY( &o2.value() != &t );
> +#endif
> +
> + return true;
> +}
> +
> +int main()
> +{
> + test();
> + static_assert(test());
> +}
> diff --git
> a/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_args_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_args_neg.cc
> new file mode 100644
> index 00000000000..6166c658c54
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_args_neg.cc
> @@ -0,0 +1,43 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <optional>
> +
> +struct C {
> + C();
> + C(int);
> +};
> +C s(10);
> +const C cs(1);
> +
> +template<typename T>
> +using decay_pre26 =
> +#if __cplusplus > 202302
> + T;
> +#else
> + std::decay_t<T>;
> +#endif
> +
> +auto z1 = std::make_optional<C&>(); // { dg-error "no matching
> function for call" }
> +auto z2 = std::make_optional<const C&>(); // { dg-error "no matching
> function for call" }
> +auto z3 = std::make_optional<C&&>(); // { dg-error "no matching
> function for call" }
> +auto z4 = std::make_optional<const C&&>(); // { dg-error "no matching
> function for call" }
> +
> +auto o1 = std::make_optional<C&>(10); // { dg-error "no matching
> function for call" }
> +auto o2 = std::make_optional<const C&>(10); // { dg-error "from here" }
> +auto o3 = std::make_optional<C&&>(10); // { dg-error "from here" }
> +auto o4 = std::make_optional<const C&&>(10); // { dg-error "from here" }
> +
> +auto t1 = std::make_optional<C&>(10, 20); // { dg-error "no
> matching function for call" }
> +auto t2 = std::make_optional<const C&>(10, 20); // { dg-error "no
> matching function for call" }
> +auto t3 = std::make_optional<C&&>(10, 20); // { dg-error "no
> matching function for call" }
> +auto t3 = std::make_optional<const C&&>(10, 20); // { dg-error "no
> matching function for call" }
> +
> +// { dg-prune-output "no type named 'type' in 'struct std::enable_if" }
> +// { dg-prune-output "type/value mismatch at argument 1 in template
> parameter list" }
> +// { dg-prune-output "in a union may not have reference type" }
> +// { dg-prune-output "static assertion failed" }
> +// { dg-prune-output "forming pointer to reference type" }
> +// { dg-prune-output "cannot bind .* reference of type" }
> +// { dg-prune-output "binding reference of type" }
> +// { dg-prune-output "no matching function for call to 'std::optional" }
> +
> diff --git
> a/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_lvalue_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_lvalue_neg.cc
> new file mode 100644
> index 00000000000..aed6791a3ff
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_lvalue_neg.cc
> @@ -0,0 +1,40 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <optional>
> +#include <type_traits>
> +
> +struct C {
> + C();
> + C(int);
> +};
> +C s(10);
> +const C cs(1);
> +
> +template<typename T>
> +using decay_pre26 =
> +#if __cplusplus > 202302
> + T;
> +#else
> + std::decay_t<T>;
> +#endif
> +
> +auto lr1 = std::make_optional<C&>(s); // changed meaning
> +static_assert( std::is_same_v< decltype(lr1),
> std::optional<decay_pre26<C&>>> );
> +auto lr2 = std::make_optional<const C&>(s); // { dg-error "here" "" {
> target c++23_down } }
> +auto lr3 = std::make_optional<C&&>(s); // { dg-error "no matching
> function for call" }
> +auto lr4 = std::make_optional<const C&&>(s); // { dg-error "no matching
> function for call" }
> +
> +auto clr1 = std::make_optional<C&>(cs); // { dg-error "no matching
> function for call" }
> +auto clr2 = std::make_optional<const C&>(cs); // changed meaning
> +static_assert( std::is_same_v< decltype(clr2),
> std::optional<decay_pre26<const C&>>> );
> +auto clr3 = std::make_optional<C&&>(cs); // { dg-error "no matching
> function for call" }
> +auto clr3 = std::make_optional<const C&&>(cs); // { dg-error "no matching
> function for call" }
> +
> +// { dg-prune-output "no type named 'type' in 'struct std::enable_if" }
> +// { dg-prune-output "type/value mismatch at argument 1 in template
> parameter list" }
> +// { dg-prune-output "in a union may not have reference type" }
> +// { dg-prune-output "static assertion failed" }
> +// { dg-prune-output "forming pointer to reference type" }
> +// { dg-prune-output "cannot bind .* reference of type" }
> +// { dg-prune-output "binding reference of type" }
> +// { dg-prune-output "no matching function for call to `std::optional" }
> diff --git
> a/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_rvalue_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_rvalue_neg.cc
> new file mode 100644
> index 00000000000..22f669ceb68
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/20_util/optional/ref/make_optional/from_rvalue_neg.cc
> @@ -0,0 +1,38 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <optional>
> +#include <type_traits>
> +
> +struct C {
> + C();
> + C(int);
> +};
> +C s(10);
> +const C cs(1);
> +
> +template<typename T>
> +using decay_pre26 =
> +#if __cplusplus > 202302
> + T;
> +#else
> + std::decay_t<T>;
> +#endif
> +
> +auto p1 = std::make_optional<C&>(C(10)); // { dg-error "no
> matching function for call" }
> +auto p2 = std::make_optional<const C&>(C(10)); // { dg-error "from here"
> }
> +auto p3 = std::make_optional<C&&>(C(10)); // { dg-error "from here"
> "" { target c++26 } }
> +auto p4 = std::make_optional<const C&&>(C(10)); // { dg-error "from here"
> }
> +
> +auto b1 = std::make_optional<C&>({10}); // { dg-error "no matching
> function for call" }
> +auto b2 = std::make_optional<const C&>({10}); // { dg-error "no matching
> function for call" "" { target c++26 } }
> +auto b3 = std::make_optional<C&&>({10}); // { dg-error "no matching
> function for call" "" { target c++26 } }
> +auto b4 = std::make_optional<const C&&>({10}); // { dg-error "no matching
> function for call" "" { target c++26 } }
> +
> +// { dg-prune-output "no type named 'type' in 'struct std::enable_if" }
> +// { dg-prune-output "type/value mismatch at argument 1 in template
> parameter list" }
> +// { dg-prune-output "in a union may not have reference type" }
> +// { dg-prune-output "static assertion failed" }
> +// { dg-prune-output "forming pointer to reference type" }
> +// { dg-prune-output "cannot bind .* reference of type" }
> +// { dg-prune-output "binding reference of type" }
> +// { dg-prune-output "no matching function for call to 'std::optional" }
> diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/monadic.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/monadic.cc
> new file mode 100644
> index 00000000000..e8460c6528b
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/monadic.cc
> @@ -0,0 +1,192 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <optional>
> +#include <type_traits>
> +#include <testsuite_hooks.h>
> +#include <utility>
> +
> +struct NonMovable
> +{
> + constexpr NonMovable() {}
> + NonMovable(NonMovable&&) = delete;
> +};
> +
> +struct Tracker
> +{
> + int copy = 0;
> + int move = 0;
> +
> + Tracker() = default;
> +
> + constexpr Tracker(Tracker const& o)
> + : copy(o.copy+1), move(o.move)
> + {}
> +
> + constexpr Tracker(Tracker&& o)
> + : copy(o.copy), move(o.move+1)
> + {}
> +
> + Tracker& operator=(Tracker) = delete;
> +
> + void reset() {
> + copy = move = 0;
> + }
> +};
> +
> +template<typename T>
> +auto identity_of = []<typename U>(U&& t) -> std::optional<T>
> +{
> + static_assert( std::is_same_v<T, U&&> );
> + VERIFY( t.copy == 0 );
> + VERIFY( t.move == 0 );
> + return std::optional<T>(t);
> +};
> +
> +constexpr void
> +test_and_then()
> +{
> + std::optional<Tracker> t(std::in_place);
> + std::optional<Tracker&> rt(t);
> + std::optional<const Tracker&> rct(t);
> +
> + auto r1 = t.and_then(identity_of<Tracker&>);
> + VERIFY( r1.has_value() );
> + VERIFY( &r1.value() == &t.value() );
> +
> + auto r2 = rt.and_then(identity_of<Tracker&>);
> + VERIFY( r2.has_value() );
> + VERIFY( &r2.value() == &t.value() );
> +
> + std::as_const(rt).and_then(identity_of<Tracker&>);
> + std::move(rt).and_then(identity_of<Tracker&>);
> +
> + auto r4 = rct.and_then(identity_of<const Tracker&>);
> + VERIFY( r4.has_value() );
> + VERIFY( &r4.value() == &t.value() );
> +
> + std::as_const(rct).and_then(identity_of<const Tracker&>);
> + std::move(rct).and_then(identity_of<const Tracker&>);
> +
> + auto r5 = rt.and_then([](Tracker&) { return std::optional<int>(42); });
> + static_assert( std::is_same_v<decltype(r5), std::optional<int>> );
> + VERIFY( r5.has_value() );
> + VERIFY( r5.value() == 42 );
> +
> + auto r6 = rct.and_then([](const Tracker&) { return
> std::optional<int>(); });
> + static_assert( std::is_same_v<decltype(r6), std::optional<int>> );
> + VERIFY( !r6.has_value() );
> +
> + rct.reset();
> + auto r7 = rct.and_then([](const Tracker&) { VERIFY(false); return
> std::optional<int>(42); });
> + static_assert( std::is_same_v<decltype(r7), std::optional<int>> );
> + VERIFY( !r7.has_value() );
> +
> + rt.reset();
> + auto r8 = rt.and_then([](Tracker&) { VERIFY(false); return
> std::optional<int>(); });
> + static_assert( std::is_same_v<decltype(r8), std::optional<int>> );
> + VERIFY( !r8.has_value() );
> +}
> +
> +template<typename T>
> +constexpr void
> +test_or_else()
> +{
> + T t, u;
> +
> + std::optional<T&> ot(t);
> + auto r1 = ot.or_else([&] { VERIFY(false); return std::optional<T&>(u);
> });
> + VERIFY( &ot.value() == &t );
> + VERIFY( r1.has_value() );
> + VERIFY( &r1.value() == &t );
> + auto r2 = std::move(ot).or_else([&] { VERIFY(false); return
> std::optional<T&>(); });
> + VERIFY( &ot.value() == &t );
> + VERIFY( r2.has_value() );
> + VERIFY( &r2.value() == &t );
> +
> + ot.reset();
> + auto r3 = ot.or_else([&] { return std::optional<T&>(u); });
> + VERIFY( !ot.has_value() );
> + VERIFY( r3.has_value() );
> + VERIFY( &r3.value() == &u );
> + auto r4 = std::move(ot).or_else([] { return std::optional<T&>(); });
> + VERIFY( !ot.has_value() );
> + VERIFY( !r4.has_value() );
> +}
> +
> +constexpr void
> +test_transform()
> +{
> + std::optional<Tracker> t(std::in_place);
> +
> + auto r1 = t.transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r1), std::optional<int&>> );
> + VERIFY( r1.has_value() );
> + VERIFY( &r1.value() == &t->copy );
> + auto r2 = std::as_const(t).transform(&Tracker::move);
> + static_assert( std::is_same_v<decltype(r2), std::optional<const int&>>
> );
> + VERIFY( r2.has_value() );
> + VERIFY( &r2.value() == &t->move );
> +
> + std::optional<Tracker&> rt(t);
> + auto r3 = rt.transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r3), std::optional<int&>> );
> + VERIFY( r3.has_value() );
> + VERIFY( &r3.value() == &t->copy );
> + auto r4 = std::as_const(rt).transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r4), std::optional<int&>> );
> + VERIFY( r4.has_value() );
> + VERIFY( &r4.value() == &t->copy );
> + auto r5 = std::move(rt).transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r5), std::optional<int&>> );
> + VERIFY( r5.has_value() );
> + VERIFY( &r5.value() == &t->copy );
> +
> + auto r6 = rt.transform([] (Tracker& t) { return 10; });
> + static_assert( std::is_same_v<decltype(r6), std::optional<int>> );
> + VERIFY( r6.has_value() );
> + VERIFY( &r6.value() != &t->copy );
> + VERIFY( r6.value() == 10 );
> +
> + auto r7 = rt.transform([] (Tracker& t) { return NonMovable(); });
> + static_assert( std::is_same_v<decltype(r7), std::optional<NonMovable>>
> );
> + VERIFY( r7.has_value() );
> +
> + rt.reset();
> + auto r8 = rt.transform([] (Tracker& t) { VERIFY(false); return 42; });
> + static_assert( std::is_same_v<decltype(r8), std::optional<int>> );
> + VERIFY( !r8.has_value() );
> +
> + std::optional<const Tracker&> crt(t);
> + auto r9 = crt.transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r9), std::optional<const int&>>
> );
> + VERIFY( r9.has_value() );
> + VERIFY( &r9.value() == &t->copy );
> + auto r10 = std::as_const(crt).transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r10), std::optional<const int&>>
> );
> + VERIFY( r10.has_value() );
> + VERIFY( &r10.value() == &t->copy );
> + auto r11 = std::move(crt).transform(&Tracker::copy);
> + static_assert( std::is_same_v<decltype(r11), std::optional<const int&>>
> );
> + VERIFY( r11.has_value() );
> + VERIFY( &r11.value() == &t->copy );
> +
> + crt.reset();
> + auto r12 = rt.transform([] (Tracker& t) { VERIFY(false); return 42; });
> + static_assert( std::is_same_v<decltype(r12), std::optional<int>> );
> + VERIFY( !r12.has_value() );
> +}
> +
> +int main()
> +{
> + auto test_all = [] {
> + test_and_then();
> + test_transform();
> + test_or_else<Tracker>();
> + test_or_else<const Tracker>();
> + test_or_else<NonMovable>();
> + return true;
> + };
> +
> + test_all();
> + static_assert(test_all());
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/optional/ref/relops.cc
> b/libstdc++-v3/testsuite/20_util/optional/ref/relops.cc
> new file mode 100644
> index 00000000000..e0b30c8e898
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/optional/ref/relops.cc
> @@ -0,0 +1,229 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <optional>
> +#include <functional>
> +#include <testsuite_hooks.h>
> +#include <type_traits>
> +
> +template<typename T, typename H = std::hash<T>>
> +constexpr bool has_disabled_hash
> + = !std::is_default_constructible_v<H>
> + && !std::is_copy_constructible_v<H>
> + && !std::is_move_constructible_v<H>
> + && !std::is_copy_assignable_v<H>
> + && !std::is_move_assignable_v<H>;
> +
> +static_assert(has_disabled_hash<std::optional<int&>>);
> +static_assert(has_disabled_hash<std::optional<const int&>>);
> +
> +template<typename T, typename V>
> +constexpr void
> +test_compare_val(V& l, V& h)
> +{
> + std::optional<T> t;
> +
> + VERIFY( !(t == l) );
> + VERIFY( (t != l) );
> + VERIFY( (t < l) );
> + VERIFY( (t <= l) );
> + VERIFY( !(t > l) );
> + VERIFY( !(t >= l) );
> + VERIFY( (t <=> l) < 0 );
> +
> + VERIFY( !(l == t) );
> + VERIFY( (l != t) );
> + VERIFY( !(l < t) );
> + VERIFY( !(l <= t) );
> + VERIFY( (l > t) );
> + VERIFY( (l >= t) );
> + VERIFY( (l <=> t) > 0 );
> +
> + t.emplace(l);
> + VERIFY( (t == l) );
> + VERIFY( !(t != l) );
> + VERIFY( !(t < l) );
> + VERIFY( (t <= l) );
> + VERIFY( !(t > l) );
> + VERIFY( (t >= l) );
> + VERIFY( (t <=> l) == 0 );
> +
> + VERIFY( (l == t) );
> + VERIFY( !(l != t) );
> + VERIFY( !(l < t) );
> + VERIFY( (l <= t) );
> + VERIFY( !(l > t) );
> + VERIFY( (l >= t) );
> + VERIFY( (t <=> l) == 0 );
> +
> + t.emplace(h);
> + VERIFY( !(t == l) );
> + VERIFY( (t != l) );
> + VERIFY( !(t < l) );
> + VERIFY( !(t <= l) );
> + VERIFY( (t > l) );
> + VERIFY( (t >= l) );
> + VERIFY( (t <=> l) > 0 );
> +
> + VERIFY( !(l == t) );
> + VERIFY( (l != t) );
> + VERIFY( (l < t) );
> + VERIFY( (l <= t) );
> + VERIFY( !(l > t) );
> + VERIFY( !(l >= t) );
> + VERIFY( (l <=> t) < 0 );
> +}
> +
> +template<typename T, typename U, typename V>
> +constexpr void
> +test_compare_opts(V& l, V& h)
> +{
> + std::optional<T> t;
> + std::optional<U> u;
> +
> + VERIFY( (t == u) );
> + VERIFY( !(t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( (t >= u) );
> + VERIFY( (t <=> u) == 0 );
> +
> + t.emplace(l);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( !(t <= u) );
> + VERIFY( (t > u) );
> + VERIFY( (t >= u) );
> + VERIFY( (t <=> u) > 0 );
> +
> + u.emplace(l);
> + VERIFY( (t == u) );
> + VERIFY( !(t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( (t <= u) );
> + VERIFY( (t <=> u) == 0 );
> +
> + u.emplace(h);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( (t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( !(t >= u) );
> + VERIFY( (t <=> u) < 0 );
> +
> + t.reset();
> + u.emplace(l);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( (t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( !(t >= u) );
> + VERIFY( (t <=> u) < 0 );
> +
> + t.emplace(h);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( !(t <= u) );
> + VERIFY( (t > u) );
> + VERIFY( (t >= u) );
> + VERIFY( (t <=> u) > 0 );
> +}
> +
> +template<typename V>
> +constexpr void
> +test_compare(V l, V h)
> +{
> + test_compare_val<V&>(l, h);
> + test_compare_val<const V&>(l, h);
> +
> + test_compare_opts<V&, V&>(l, h);
> + test_compare_opts<V, V&>(l, h);
> + test_compare_opts<V&, V>(l, h);
> +
> + test_compare_opts<const V&, const V&>(l, h);
> + test_compare_opts<V, const V&>(l, h);
> + test_compare_opts<const V&, V>(l, h);
> +
> + test_compare_opts<V&, const V&>(l, h);
> + test_compare_opts<const V&, V&>(l, h);
> +}
> +
> +struct TreeWay
> +{
> + int v;
> + friend auto operator<=>(TreeWay, TreeWay) = default;
> +};
> +
> +struct Other
> +{
> + int v;
> +
> + constexpr Other(int p) : v(p) {}
> + constexpr Other(TreeWay p) : v(p.v) {}
> +
> + friend bool operator==(Other, Other) = default;
> + friend auto operator<=>(Other, Other) = default;
> +
> + friend constexpr bool
> + operator==(const Other& lhs, const TreeWay& rhs)
> + { return lhs.v == rhs.v; }
> +
> + friend constexpr std::strong_ordering
> + operator<=>(const Other& lhs, const TreeWay& rhs)
> + { return lhs.v <=> rhs.v; }
> +};
> +
> +constexpr void
> +test_heterogeneus_cmp()
> +{
> + TreeWay l{10};
> + Other h{20};
> +
> + std::optional<TreeWay&> t;
> + std::optional<const Other&> u;
> +
> + VERIFY( (t == u) );
> + VERIFY( !(t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( (t >= u) );
> + VERIFY( (t <=> u) == 0 );
> +
> + t.emplace(l);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( !(t < u) );
> + VERIFY( !(t <= u) );
> + VERIFY( (t > u) );
> + VERIFY( (t >= u) );
> + VERIFY( (t <=> u) > 0 );
> +
> + u.emplace(h);
> + VERIFY( !(t == u) );
> + VERIFY( (t != u) );
> + VERIFY( (t < u) );
> + VERIFY( (t <= u) );
> + VERIFY( !(t > u) );
> + VERIFY( !(t >= u) );
> + VERIFY( (t <=> u) < 0 );
> +}
> +
> +int main()
> +{
> + auto test_all = [] {
> + test_compare(2, 5);
> + test_compare(TreeWay{11}, TreeWay{12});
> + test_heterogeneus_cmp();
> + return true;
> + };
> +
> + test_all();
> + static_assert(test_all());
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/optional/relops/constrained.cc
> b/libstdc++-v3/testsuite/20_util/optional/relops/constrained.cc
> index 3e393257928..ec47552c475 100644
> --- a/libstdc++-v3/testsuite/20_util/optional/relops/constrained.cc
> +++ b/libstdc++-v3/testsuite/20_util/optional/relops/constrained.cc
> @@ -8,8 +8,8 @@
> # error "Feature-test macro for constrained_equality has wrong value"
> #endif
>
> -template<typename T, typename U = T>
> -concept eq_comparable
> +template<typename T, typename U>
> +concept eq_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t == u;
> *t == u;
> @@ -17,7 +17,19 @@ concept eq_comparable
> };
>
> template<typename T, typename U = T>
> -concept ne_comparable
> +concept eq_comparable =
> + eq_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && eq_comparable_impl<T&, U&>
> + && eq_comparable_impl<T const&, U const&>
> + && eq_comparable_impl<T const&, U&>
> + && eq_comparable_impl<T, U const&>
> + && eq_comparable_impl<T&, U>
> +#endif
> +;
> +
> +template<typename T, typename U>
> +concept ne_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t != u;
> *t != u;
> @@ -25,7 +37,19 @@ concept ne_comparable
> };
>
> template<typename T, typename U = T>
> -concept lt_comparable
> +concept ne_comparable =
> + ne_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && ne_comparable_impl<T&, U&>
> + && ne_comparable_impl<T const&, U const&>
> + && ne_comparable_impl<T const&, U&>
> + && ne_comparable_impl<T, U const&>
> + && ne_comparable_impl<T&, U>
> +#endif
> +;
> +
> +template<typename T, typename U>
> +concept lt_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t < u;
> *t < u;
> @@ -33,7 +57,19 @@ concept lt_comparable
> };
>
> template<typename T, typename U = T>
> -concept le_comparable
> +concept lt_comparable =
> + lt_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && lt_comparable_impl<T&, U&>
> + && lt_comparable_impl<T const&, U const&>
> + && lt_comparable_impl<T const&, U&>
> + && lt_comparable_impl<T, U const&>
> + && lt_comparable_impl<T&, U>
> +#endif
> +;
> +
> +template<typename T, typename U>
> +concept le_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t <= u;
> *t <= u;
> @@ -41,7 +77,19 @@ concept le_comparable
> };
>
> template<typename T, typename U = T>
> -concept gt_comparable
> +concept le_comparable =
> + le_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && le_comparable_impl<T&, U&>
> + && le_comparable_impl<T const&, U const&>
> + && le_comparable_impl<T const&, U&>
> + && le_comparable_impl<T, U const&>
> + && le_comparable_impl<T&, U>
> +#endif
> +;
> +
> +template<typename T, typename U>
> +concept gt_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t > u;
> *t > u;
> @@ -49,13 +97,37 @@ concept gt_comparable
> };
>
> template<typename T, typename U = T>
> -concept ge_comparable
> +concept gt_comparable =
> + gt_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && gt_comparable_impl<T&, U&>
> + && gt_comparable_impl<T const&, U const&>
> + && gt_comparable_impl<T const&, U&>
> + && gt_comparable_impl<T, U const&>
> + && gt_comparable_impl<T&, U>
> +#endif
> +;
> +
> +template<typename T, typename U>
> +concept ge_comparable_impl
> = requires (const std::optional<T>& t, const std::optional<U>& u) {
> t >= u;
> *t >= u;
> t >= *u;
> };
>
> +template<typename T, typename U = T>
> +concept ge_comparable =
> + ge_comparable_impl<T, U>
> +#if __cplusplus > 202302l
> + && ge_comparable_impl<T&, U&>
> + && ge_comparable_impl<T const&, U const&>
> + && ge_comparable_impl<T const&, U&>
> + && ge_comparable_impl<T, U const&>
> + && ge_comparable_impl<T&, U>
> +#endif
> +;
> +
> static_assert( eq_comparable<int> );
> static_assert( ne_comparable<int> );
> static_assert( lt_comparable<int> );
> diff --git a/libstdc++-v3/testsuite/20_util/optional/requirements.cc
> b/libstdc++-v3/testsuite/20_util/optional/requirements.cc
> index 68e59057b5e..9e8cf83da44 100644
> --- a/libstdc++-v3/testsuite/20_util/optional/requirements.cc
> +++ b/libstdc++-v3/testsuite/20_util/optional/requirements.cc
> @@ -26,8 +26,10 @@
> # error "Feature test macro for optional has wrong value in <optional>"
> #elif __cplusplus == 202002L && __cpp_lib_optional != 202106L
> # error "Feature test macro for optional has wrong value for C++20 in
> <optional>"
> -#elif __cplusplus > 202002L && __cpp_lib_optional != 202110L
> -# error "Feature test macro for optional has wrong value for C++23 in
> <version>"
> +#elif __cplusplus == 202302L && __cpp_lib_optional != 202110L
> +# error "Feature test macro for optional has wrong value for C++23 in
> <optional>"
> +#elif __cplusplus > 202302L && __cpp_lib_optional != 202506L
> +# error "Feature test macro for optional has wrong value for C++26 in
> <optional>"
> #endif
>
> #include <testsuite_hooks.h>
> diff --git a/libstdc++-v3/testsuite/20_util/optional/requirements_neg.cc
> b/libstdc++-v3/testsuite/20_util/optional/requirements_neg.cc
> index 688c305803e..142fbbfc515 100644
> --- a/libstdc++-v3/testsuite/20_util/optional/requirements_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/optional/requirements_neg.cc
> @@ -2,17 +2,32 @@
>
> #include <optional>
>
> +// C++ < 26:
> // T shall be a type other than cv in_place_t or cv nullopt_t
> // that meets the Cpp17Destructible requirements
> +// C++ >= 26:
> +// A type X is a valid contained type for optional if X is an lvalue
> reference
> +// type or a complete non-array object type, and remove_cvref_t<X> is a
> type
> +// other than in_place_t or nullopt_t. If a specialization of optional
> +// is instantiated with a type T that is not a valid contained type for
> +// optional, the program is ill-formed. If T is an object type,
> +// T shall meet the Cpp17Destructible requirements
>
> std::optional<std::nullopt_t> o1; // { dg-error "here" }
> std::optional<const std::nullopt_t> o2; // { dg-error "here" }
> std::optional<std::in_place_t> o3; // { dg-error "here" }
> std::optional<const std::in_place_t> o4; // { dg-error "here" }
> -std::optional<int&> o5; // { dg-error "here" }
> +std::optional<int&> o5; // { dg-error "here"
> "optional<T&> is a C++26 feature" { target c++23_down } }
> std::optional<int[1]> o6; // { dg-error "here" }
> std::optional<int[]> o7; // { dg-error "here" }
> std::optional<int()> o8; // { dg-error "here" }
> +std::optional<const int &> o9; // { dg-error "here"
> "optional<T&> is a C++26 feature" { target c++23_down } }
> +std::optional<std::in_place_t &> o10; // { dg-error "here" }
> +std::optional<const std::in_place_t &> o11; // { dg-error "here" }
> +std::optional<std::nullopt_t &> o12; // { dg-error "here" }
> +std::optional<const std::nullopt_t &> o13; // { dg-error "here" }
> +std::optional<int &&> o14; // { dg-error "here" }
> +std::optional<const int &&> o15; // { dg-error "here" }
>
> // { dg-error "static assertion failed" "" { target *-*-* } 0 }
>
> diff --git a/libstdc++-v3/testsuite/20_util/optional/version.cc
> b/libstdc++-v3/testsuite/20_util/optional/version.cc
> index ba44aa52535..ae9339a01af 100644
> --- a/libstdc++-v3/testsuite/20_util/optional/version.cc
> +++ b/libstdc++-v3/testsuite/20_util/optional/version.cc
> @@ -9,8 +9,10 @@
> # error "Feature test macro for optional has wrong value for C++17 in
> <version>"
> #elif __cplusplus == 202002L && __cpp_lib_optional != 202106L
> # error "Feature test macro for optional has wrong value for C++20 in
> <version>"
> -#elif __cplusplus > 202002L && __cpp_lib_optional != 202110L
> +#elif __cplusplus == 202302L && __cpp_lib_optional != 202110L
> # error "Feature test macro for optional has wrong value for C++23 in
> <version>"
> +#elif __cplusplus > 202302L && __cpp_lib_optional != 202506L
> +# error "Feature test macro for optional has wrong value for C++26 in
> <version>"
> #endif
>
> #if __cplusplus >= 202302L
> --
> 2.51.0
>
>
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