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[libc++][NFC] Make enable_ifs in <optional> consistent (llvm#127184)
We've documented the preferred `enable_if` style in the coding guidelines. This updates `<optional>` to conform to them
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‎libcxx/include/optional‎

Lines changed: 114 additions & 121 deletions
Original file line numberDiff line numberDiff line change
@@ -672,44 +672,41 @@ public:
672672
_LIBCPP_HIDE_FROM_ABI constexpr optional(optional&&) = default;
673673
_LIBCPP_HIDE_FROM_ABI constexpr optional(nullopt_t) noexcept {}
674674

675-
template <
676-
class _InPlaceT,
677-
class... _Args,
678-
class = enable_if_t< _And< _IsSame<_InPlaceT, in_place_t>, is_constructible<value_type, _Args...> >::value > >
675+
template <class _InPlaceT,
676+
class... _Args,
677+
enable_if_t<_And<_IsSame<_InPlaceT, in_place_t>, is_constructible<value_type, _Args...>>::value, int> = 0>
679678
_LIBCPP_HIDE_FROM_ABI constexpr explicit optional(_InPlaceT, _Args&&... __args)
680679
: __base(in_place, std::forward<_Args>(__args)...) {}
681680

682681
template <class _Up,
683682
class... _Args,
684-
class = enable_if_t< is_constructible_v<value_type, initializer_list<_Up>&, _Args...>> >
683+
enable_if_t<is_constructible_v<value_type, initializer_list<_Up>&, _Args...>, int> = 0>
685684
_LIBCPP_HIDE_FROM_ABI constexpr explicit optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
686685
: __base(in_place, __il, std::forward<_Args>(__args)...) {}
687686

688-
template <class _Up = value_type,
689-
enable_if_t< _CheckOptionalArgsCtor<_Up>::template __enable_implicit<_Up>(), int> = 0>
687+
template <class _Up = value_type,
688+
enable_if_t<_CheckOptionalArgsCtor<_Up>::template __enable_implicit<_Up>(), int> = 0>
690689
_LIBCPP_HIDE_FROM_ABI constexpr optional(_Up&& __v) : __base(in_place, std::forward<_Up>(__v)) {}
691690

692-
template <class _Up, enable_if_t< _CheckOptionalArgsCtor<_Up>::template __enable_explicit<_Up>(), int> = 0>
691+
template <class _Up, enable_if_t<_CheckOptionalArgsCtor<_Up>::template __enable_explicit<_Up>(), int> = 0>
693692
_LIBCPP_HIDE_FROM_ABI constexpr explicit optional(_Up&& __v) : __base(in_place, std::forward<_Up>(__v)) {}
694693

695694
// LWG2756: conditionally explicit conversion from const optional<_Up>&
696-
template <class _Up,
697-
enable_if_t< _CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_implicit<_Up>(), int> = 0>
695+
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_implicit<_Up>(), int> = 0>
698696
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional(const optional<_Up>& __v) {
699697
this->__construct_from(__v);
700698
}
701-
template <class _Up,
702-
enable_if_t< _CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_explicit<_Up>(), int> = 0>
699+
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_explicit<_Up>(), int> = 0>
703700
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit optional(const optional<_Up>& __v) {
704701
this->__construct_from(__v);
705702
}
706703

707704
// LWG2756: conditionally explicit conversion from optional<_Up>&&
708-
template <class _Up, enable_if_t< _CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_implicit<_Up>(), int> = 0>
705+
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_implicit<_Up>(), int> = 0>
709706
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional(optional<_Up>&& __v) {
710707
this->__construct_from(std::move(__v));
711708
}
712-
template <class _Up, enable_if_t< _CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_explicit<_Up>(), int> = 0>
709+
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_explicit<_Up>(), int> = 0>
713710
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit optional(optional<_Up>&& __v) {
714711
this->__construct_from(std::move(__v));
715712
}
@@ -718,7 +715,7 @@ public:
718715
template <class _Tag,
719716
class _Fp,
720717
class... _Args,
721-
__enable_if_t<_IsSame<_Tag, __optional_construct_from_invoke_tag>::value, int> = 0>
718+
enable_if_t<_IsSame<_Tag, __optional_construct_from_invoke_tag>::value, int> = 0>
722719
_LIBCPP_HIDE_FROM_ABI constexpr explicit optional(_Tag, _Fp&& __f, _Args&&... __args)
723720
: __base(__optional_construct_from_invoke_tag{}, std::forward<_Fp>(__f), std::forward<_Args>(__args)...) {}
724721
# endif
@@ -732,12 +729,12 @@ public:
732729
_LIBCPP_HIDE_FROM_ABI constexpr optional& operator=(optional&&) = default;
733730

734731
// LWG2756
735-
template <
736-
class _Up = value_type,
737-
class = enable_if_t< _And< _IsNotSame<__remove_cvref_t<_Up>, optional>,
738-
_Or< _IsNotSame<__remove_cvref_t<_Up>, value_type>, _Not<is_scalar<value_type>> >,
739-
is_constructible<value_type, _Up>,
740-
is_assignable<value_type&, _Up> >::value> >
732+
template <class _Up = value_type,
733+
enable_if_t<_And<_IsNotSame<__remove_cvref_t<_Up>, optional>,
734+
_Or<_IsNotSame<__remove_cvref_t<_Up>, value_type>, _Not<is_scalar<value_type>>>,
735+
is_constructible<value_type, _Up>,
736+
is_assignable<value_type&, _Up>>::value,
737+
int> = 0>
741738
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional& operator=(_Up&& __v) {
742739
if (this->has_value())
743740
this->__get() = std::forward<_Up>(__v);
@@ -747,21 +744,20 @@ public:
747744
}
748745

749746
// LWG2756
750-
template <class _Up,
751-
enable_if_t< _CheckOptionalLikeAssign<_Up, _Up const&>::template __enable_assign<_Up>(), int> = 0>
747+
template <class _Up, enable_if_t<_CheckOptionalLikeAssign<_Up, _Up const&>::template __enable_assign<_Up>(), int> = 0>
752748
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional& operator=(const optional<_Up>& __v) {
753749
this->__assign_from(__v);
754750
return *this;
755751
}
756752

757753
// LWG2756
758-
template <class _Up, enable_if_t< _CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_assign<_Up>(), int> = 0>
754+
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up&&>::template __enable_assign<_Up>(), int> = 0>
759755
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional& operator=(optional<_Up>&& __v) {
760756
this->__assign_from(std::move(__v));
761757
return *this;
762758
}
763759

764-
template <class... _Args, class = enable_if_t< is_constructible_v<value_type, _Args...> > >
760+
template <class... _Args, enable_if_t<is_constructible_v<value_type, _Args...>, int> = 0>
765761
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(_Args&&... __args) {
766762
reset();
767763
this->__construct(std::forward<_Args>(__args)...);
@@ -770,7 +766,7 @@ public:
770766

771767
template <class _Up,
772768
class... _Args,
773-
class = enable_if_t< is_constructible_v<value_type, initializer_list<_Up>&, _Args...> > >
769+
enable_if_t<is_constructible_v<value_type, initializer_list<_Up>&, _Args...>, int> = 0>
774770
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) {
775771
reset();
776772
this->__construct(__il, std::forward<_Args>(__args)...);
@@ -982,77 +978,75 @@ public:
982978
using __base::reset;
983979
};
984980

985-
# if _LIBCPP_STD_VER >= 17
986981
template <class _Tp>
987982
optional(_Tp) -> optional<_Tp>;
988-
# endif
989983

990984
// Comparisons between optionals
991-
template <class _Tp, class _Up>
992-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
993-
is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
994-
bool >
995-
operator==(const optional<_Tp>& __x, const optional<_Up>& __y) {
985+
template <
986+
class _Tp,
987+
class _Up,
988+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>, int> = 0>
989+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const optional<_Tp>& __x, const optional<_Up>& __y) {
996990
if (static_cast<bool>(__x) != static_cast<bool>(__y))
997991
return false;
998992
if (!static_cast<bool>(__x))
999993
return true;
1000994
return *__x == *__y;
1001995
}
1002996

1003-
template <class _Tp, class _Up>
1004-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1005-
is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
1006-
bool >
1007-
operator!=(const optional<_Tp>& __x, const optional<_Up>& __y) {
997+
template <
998+
class _Tp,
999+
class _Up,
1000+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>, int> = 0>
1001+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const optional<_Tp>& __x, const optional<_Up>& __y) {
10081002
if (static_cast<bool>(__x) != static_cast<bool>(__y))
10091003
return true;
10101004
if (!static_cast<bool>(__x))
10111005
return false;
10121006
return *__x != *__y;
10131007
}
10141008

1015-
template <class _Tp, class _Up>
1016-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1017-
is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
1018-
bool >
1019-
operator<(const optional<_Tp>& __x, const optional<_Up>& __y) {
1009+
template <
1010+
class _Tp,
1011+
class _Up,
1012+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>, int> = 0>
1013+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const optional<_Tp>& __x, const optional<_Up>& __y) {
10201014
if (!static_cast<bool>(__y))
10211015
return false;
10221016
if (!static_cast<bool>(__x))
10231017
return true;
10241018
return *__x < *__y;
10251019
}
10261020

1027-
template <class _Tp, class _Up>
1028-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1029-
is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
1030-
bool >
1031-
operator>(const optional<_Tp>& __x, const optional<_Up>& __y) {
1021+
template <
1022+
class _Tp,
1023+
class _Up,
1024+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>, int> = 0>
1025+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const optional<_Tp>& __x, const optional<_Up>& __y) {
10321026
if (!static_cast<bool>(__x))
10331027
return false;
10341028
if (!static_cast<bool>(__y))
10351029
return true;
10361030
return *__x > *__y;
10371031
}
10381032

1039-
template <class _Tp, class _Up>
1040-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1041-
is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
1042-
bool >
1043-
operator<=(const optional<_Tp>& __x, const optional<_Up>& __y) {
1033+
template <
1034+
class _Tp,
1035+
class _Up,
1036+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>, int> = 0>
1037+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const optional<_Tp>& __x, const optional<_Up>& __y) {
10441038
if (!static_cast<bool>(__x))
10451039
return true;
10461040
if (!static_cast<bool>(__y))
10471041
return false;
10481042
return *__x <= *__y;
10491043
}
10501044

1051-
template <class _Tp, class _Up>
1052-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1053-
is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
1054-
bool >
1055-
operator>=(const optional<_Tp>& __x, const optional<_Up>& __y) {
1045+
template <
1046+
class _Tp,
1047+
class _Up,
1048+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>, int> = 0>
1049+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const optional<_Tp>& __x, const optional<_Up>& __y) {
10561050
if (!static_cast<bool>(__y))
10571051
return true;
10581052
if (!static_cast<bool>(__x))
@@ -1145,99 +1139,99 @@ _LIBCPP_HIDE_FROM_ABI constexpr strong_ordering operator<=>(const optional<_Tp>&
11451139
# endif // _LIBCPP_STD_VER <= 17
11461140

11471141
// Comparisons with T
1148-
template <class _Tp, class _Up>
1149-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1150-
is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
1151-
bool >
1152-
operator==(const optional<_Tp>& __x, const _Up& __v) {
1142+
template <
1143+
class _Tp,
1144+
class _Up,
1145+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>, int> = 0>
1146+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const optional<_Tp>& __x, const _Up& __v) {
11531147
return static_cast<bool>(__x) ? *__x == __v : false;
11541148
}
11551149

1156-
template <class _Tp, class _Up>
1157-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1158-
is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
1159-
bool >
1160-
operator==(const _Tp& __v, const optional<_Up>& __x) {
1150+
template <
1151+
class _Tp,
1152+
class _Up,
1153+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>, int> = 0>
1154+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const _Tp& __v, const optional<_Up>& __x) {
11611155
return static_cast<bool>(__x) ? __v == *__x : false;
11621156
}
11631157

1164-
template <class _Tp, class _Up>
1165-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1166-
is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
1167-
bool >
1168-
operator!=(const optional<_Tp>& __x, const _Up& __v) {
1158+
template <
1159+
class _Tp,
1160+
class _Up,
1161+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>, int> = 0>
1162+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const optional<_Tp>& __x, const _Up& __v) {
11691163
return static_cast<bool>(__x) ? *__x != __v : true;
11701164
}
11711165

1172-
template <class _Tp, class _Up>
1173-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1174-
is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
1175-
bool >
1176-
operator!=(const _Tp& __v, const optional<_Up>& __x) {
1166+
template <
1167+
class _Tp,
1168+
class _Up,
1169+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>, int> = 0>
1170+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const _Tp& __v, const optional<_Up>& __x) {
11771171
return static_cast<bool>(__x) ? __v != *__x : true;
11781172
}
11791173

1180-
template <class _Tp, class _Up>
1181-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1182-
is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
1183-
bool >
1184-
operator<(const optional<_Tp>& __x, const _Up& __v) {
1174+
template <
1175+
class _Tp,
1176+
class _Up,
1177+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>, int> = 0>
1178+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const optional<_Tp>& __x, const _Up& __v) {
11851179
return static_cast<bool>(__x) ? *__x < __v : true;
11861180
}
11871181

1188-
template <class _Tp, class _Up>
1189-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1190-
is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
1191-
bool >
1192-
operator<(const _Tp& __v, const optional<_Up>& __x) {
1182+
template <
1183+
class _Tp,
1184+
class _Up,
1185+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>, int> = 0>
1186+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const _Tp& __v, const optional<_Up>& __x) {
11931187
return static_cast<bool>(__x) ? __v < *__x : false;
11941188
}
11951189

1196-
template <class _Tp, class _Up>
1197-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1198-
is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
1199-
bool >
1200-
operator<=(const optional<_Tp>& __x, const _Up& __v) {
1190+
template <
1191+
class _Tp,
1192+
class _Up,
1193+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>, int> = 0>
1194+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const optional<_Tp>& __x, const _Up& __v) {
12011195
return static_cast<bool>(__x) ? *__x <= __v : true;
12021196
}
12031197

1204-
template <class _Tp, class _Up>
1205-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1206-
is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
1207-
bool >
1208-
operator<=(const _Tp& __v, const optional<_Up>& __x) {
1198+
template <
1199+
class _Tp,
1200+
class _Up,
1201+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>, int> = 0>
1202+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const _Tp& __v, const optional<_Up>& __x) {
12091203
return static_cast<bool>(__x) ? __v <= *__x : false;
12101204
}
12111205

1212-
template <class _Tp, class _Up>
1213-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1214-
is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
1215-
bool >
1216-
operator>(const optional<_Tp>& __x, const _Up& __v) {
1206+
template <
1207+
class _Tp,
1208+
class _Up,
1209+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>, int> = 0>
1210+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const optional<_Tp>& __x, const _Up& __v) {
12171211
return static_cast<bool>(__x) ? *__x > __v : false;
12181212
}
12191213

1220-
template <class _Tp, class _Up>
1221-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1222-
is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
1223-
bool >
1224-
operator>(const _Tp& __v, const optional<_Up>& __x) {
1214+
template <
1215+
class _Tp,
1216+
class _Up,
1217+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>, int> = 0>
1218+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const _Tp& __v, const optional<_Up>& __x) {
12251219
return static_cast<bool>(__x) ? __v > *__x : true;
12261220
}
12271221

1228-
template <class _Tp, class _Up>
1229-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1230-
is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
1231-
bool >
1232-
operator>=(const optional<_Tp>& __x, const _Up& __v) {
1222+
template <
1223+
class _Tp,
1224+
class _Up,
1225+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>, int> = 0>
1226+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const optional<_Tp>& __x, const _Up& __v) {
12331227
return static_cast<bool>(__x) ? *__x >= __v : false;
12341228
}
12351229

1236-
template <class _Tp, class _Up>
1237-
_LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<
1238-
is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
1239-
bool >
1240-
operator>=(const _Tp& __v, const optional<_Up>& __x) {
1230+
template <
1231+
class _Tp,
1232+
class _Up,
1233+
enable_if_t<is_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>, int> = 0>
1234+
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const _Tp& __v, const optional<_Up>& __x) {
12411235
return static_cast<bool>(__x) ? __v >= *__x : true;
12421236
}
12431237

@@ -1252,9 +1246,8 @@ operator<=>(const optional<_Tp>& __x, const _Up& __v) {
12521246

12531247
# endif // _LIBCPP_STD_VER >= 20
12541248

1255-
template <class _Tp>
1256-
inline _LIBCPP_HIDE_FROM_ABI
1257-
_LIBCPP_CONSTEXPR_SINCE_CXX20 enable_if_t< is_move_constructible_v<_Tp> && is_swappable_v<_Tp>, void >
1249+
template <class _Tp, enable_if_t< is_move_constructible_v<_Tp> && is_swappable_v<_Tp>, int> = 0>
1250+
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
12581251
swap(optional<_Tp>& __x, optional<_Tp>& __y) noexcept(noexcept(__x.swap(__y))) {
12591252
__x.swap(__y);
12601253
}

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