https://gcc.gnu.org/g:6d86486292acbeeeda16b4f69455143391845706
commit r15-2309-g6d86486292acbeeeda16b4f69455143391845706
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Tue Jul 23 12:45:37 2024 +0100
libstdc++: Use concepts and conditional explicit in std::optional
For C++20 mode we can improve compile times by using conditional
explicit to reduce the number of constructor overloads. We can also use
requires-clauses instead of SFINAE to implement constraints on the
constructors and assignment operators.
libstdc++-v3/ChangeLog:
* include/std/optional (optional): Use C++20 features to
simplify overload sets for constructors and assignment
operators.
Diff:
---
libstdc++-v3/include/std/optional | 130 +++++++++++++++++++++++++++++++++++---
1 file changed, 121 insertions(+), 9 deletions(-)
diff --git a/libstdc++-v3/include/std/optional
b/libstdc++-v3/include/std/optional
index 700e7047abae..2cc0221865e3 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -768,6 +768,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
is_assignable<_Tp&, const optional<_Up>&&>,
is_assignable<_Tp&, optional<_Up>&&>>;
+#if __cpp_concepts && __cpp_conditional_explicit && __glibcxx_remove_cvref
+# define _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL 1
+#endif
+
/**
* @brief Class template for optional values.
*/
@@ -794,17 +798,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using _Base = _Optional_base<_Tp>;
// SFINAE helpers
- template<typename _Up>
- using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
- template<typename _Up>
- using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
- template<typename... _Cond>
- using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3836. std::expected<bool, E1> conversion constructor
// expected(const expected<U, G>&) should take precedence over
// expected(U&&) with operator bool
+#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+ template<typename _From, typename = remove_cv_t<_Tp>>
+ static constexpr bool __not_constructing_bool_from_optional
+ = true;
+
+ // If T is cv bool, remove_cvref_t<U> is not a specialization of optional
+ // i.e. do not initialize a bool from optional<U>::operator bool().
+ template<typename _From>
+ static constexpr bool
+ __not_constructing_bool_from_optional<_From, bool>
+ = !__is_optional_v<remove_cvref_t<_From>>;
+
+ // If T is not cv bool, converts-from-any-cvref<T, optional<U>> is false.
+ // The constructor that converts from optional<U> is disabled if the
+ // contained value can be initialized from optional<U>, so that the
+ // optional(U&&) constructor can be used instead.
+ template<typename _From, typename = remove_cv_t<_Tp>>
+ static constexpr bool __construct_from_contained_value
+ = !__converts_from_optional<_Tp, _From>::value;
+
+ // However, optional<U> can always be converted to bool, so don't apply
+ // this constraint when T is cv bool.
+ template<typename _From>
+ static constexpr bool __construct_from_contained_value<_From, bool>
+ = true;
+#else
template<typename _From, typename = remove_cv_t<_Tp>>
struct __not_constructing_bool_from_optional
: true_type
@@ -825,6 +849,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: true_type
{ };
+ template<typename _Up>
+ using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
+ template<typename _Up>
+ using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
+ template<typename _Up>
+ using __is_bool = is_same<remove_cv_t<_Up>, bool>;
+ template<typename... _Cond>
+ using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
+#endif
+
public:
using value_type = _Tp;
@@ -833,6 +867,58 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr optional(nullopt_t) noexcept { }
// Converting constructors for engaged optionals.
+#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+ template<typename _Up = _Tp>
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && (!is_same_v<in_place_t, remove_cvref_t<_Up>>)
+ && is_constructible_v<_Tp, _Up>
+ && __not_constructing_bool_from_optional<_Up>
+ constexpr explicit(!is_convertible_v<_Up, _Tp>)
+ optional(_Up&& __t)
+ noexcept(is_nothrow_constructible_v<_Tp, _Up>)
+ : _Base(std::in_place, std::forward<_Up>(__t)) { }
+
+ template<typename _Up>
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && is_constructible_v<_Tp, const _Up&>
+ && __construct_from_contained_value<_Up>
+ constexpr explicit(!is_convertible_v<const _Up&, _Tp>)
+ optional(const optional<_Up>& __t)
+ noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
+ {
+ if (__t)
+ emplace(__t._M_get());
+ }
+
+ template<typename _Up>
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && is_constructible_v<_Tp, _Up>
+ && __construct_from_contained_value<_Up>
+ constexpr explicit(!is_convertible_v<_Up, _Tp>)
+ optional(optional<_Up>&& __t)
+ noexcept(is_nothrow_constructible_v<_Tp, _Up>)
+ {
+ if (__t)
+ emplace(std::move(__t._M_get()));
+ }
+
+ template<typename... _Args>
+ requires is_constructible_v<_Tp, _Args...>
+ explicit constexpr
+ optional(in_place_t, _Args&&... __args)
+ noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
+ : _Base(std::in_place, std::forward<_Args>(__args)...)
+ { }
+
+ template<typename _Up, typename... _Args>
+ requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
+ explicit constexpr
+ optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
+ noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
+ _Args...>)
+ : _Base(std::in_place, __il, std::forward<_Args>(__args)...)
+ { }
+#else
template<typename _Up = _Tp,
_Requires<__not_self<_Up>, __not_tag<_Up>,
is_constructible<_Tp, _Up>,
@@ -921,6 +1007,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
_Args...>)
: _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
+#endif
// Assignment operators.
_GLIBCXX20_CONSTEXPR optional&
@@ -931,13 +1018,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename _Up = _Tp>
- _GLIBCXX20_CONSTEXPR
+#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && (!(is_scalar_v<_Tp> && is_same_v<_Tp, decay_t<_Up>>))
+ && is_constructible_v<_Tp, _Up>
+ && is_assignable_v<_Tp&, _Up>
+ constexpr optional&
+#else
enable_if_t<__and_v<__not_self<_Up>,
__not_<__and_<is_scalar<_Tp>,
is_same<_Tp, decay_t<_Up>>>>,
is_constructible<_Tp, _Up>,
is_assignable<_Tp&, _Up>>,
optional&>
+#endif
operator=(_Up&& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
is_nothrow_assignable<_Tp&, _Up>>)
@@ -951,13 +1045,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename _Up>
- _GLIBCXX20_CONSTEXPR
+#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && is_constructible_v<_Tp, const _Up&>
+ && is_assignable_v<_Tp&, const _Up&>
+ && (!__converts_from_optional<_Tp, _Up>::value)
+ && (!__assigns_from_optional<_Tp, _Up>::value)
+ constexpr optional&
+#else
enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
is_assignable<_Tp&, const _Up&>,
__not_<__converts_from_optional<_Tp, _Up>>,
__not_<__assigns_from_optional<_Tp, _Up>>>,
optional&>
+#endif
operator=(const optional<_Up>& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
is_nothrow_assignable<_Tp&, const _Up&>>)
@@ -977,13 +1079,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename _Up>
- _GLIBCXX20_CONSTEXPR
+#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+ requires (!is_same_v<optional, remove_cvref_t<_Up>>)
+ && is_constructible_v<_Tp, _Up>
+ && is_assignable_v<_Tp&, _Up>
+ && (!__converts_from_optional<_Tp, _Up>::value)
+ && (!__assigns_from_optional<_Tp, _Up>::value)
+ constexpr optional&
+#else
enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
is_assignable<_Tp&, _Up>,
__not_<__converts_from_optional<_Tp, _Up>>,
__not_<__assigns_from_optional<_Tp, _Up>>>,
optional&>
+#endif
operator=(optional<_Up>&& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
is_nothrow_assignable<_Tp&, _Up>>)
@@ -1654,6 +1764,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template <typename _Tp> optional(_Tp) -> optional<_Tp>;
#endif
+#undef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
