On Tue, 21 Oct 2025 at 08:58, Tomasz Kaminski <[email protected]> wrote:
>
>
>
> On Tue, Oct 21, 2025 at 9:27 AM Jonathan Wakely <[email protected]> wrote:
>>
>>
>>
>> On Fri, 17 Oct 2025, 16:17 Tomasz Kamiński, <[email protected]> wrote:
>>>
>>> From: Giuseppe D'Angelo <[email protected]>
>>>
>>> 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.
Yes, I would prefer that. The optimizer should be able to remove the
redundant assertions, but that won't happen at -O0, and adding more
work for the optimizer makes it less likely that things will be fully
inlined.
>>
>>
>>
>>> 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 <[email protected]>
>>> ---
>>> 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;
