[PATCH 1/2] libstdc++: Implement optional<T&> from P2988R12 [PR121748]
Tomasz Kaminski
tkaminsk@redhat.com
Tue Oct 21 07:57:29 GMT 2025
On Tue, Oct 21, 2025 at 9:27 AM Jonathan Wakely <jwakely.gcc@gmail.com>
wrote:
>
>
> On Fri, 17 Oct 2025, 16:17 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*()
>
>
>
> Doesn't this mean repeating the !empty assertion even though we already
> checked it?
>
Yes, it does. I assume the optimizer will be able to remove it. I can add
another _M_fwd
function to both, to avoid that.
>
>
> 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>
>> ---
>> 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;
>>
>
> This should repeat the extra_cond on the previous value, otherwise we'd
> define it to > 202110 even though the monadic ops aren't supported.
>
>
> + };
>> + 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;
>
>
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