[libc++] Remove a bunch of forward declarations from __tree and simplify __is_tree_value_type (#152451)

Author: philnik777

libcxx/include/__tree

@@ -27,15 +27,13 @@
 #include <__type_traits/copy_cvref.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/invoke.h>
-#include <__type_traits/is_const.h>
 #include <__type_traits/is_constructible.h>
 #include <__type_traits/is_nothrow_assignable.h>
 #include <__type_traits/is_nothrow_constructible.h>
 #include <__type_traits/is_same.h>
+#include <__type_traits/is_specialization.h>
 #include <__type_traits/is_swappable.h>
 #include <__type_traits/remove_const.h>
-#include <__type_traits/remove_const_ref.h>
-#include <__type_traits/remove_cvref.h>
 #include <__utility/forward.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
@@ -51,13 +49,6 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Tp, class _Compare, class _Allocator>
-class __tree;
-template <class _Tp, class _NodePtr, class _DiffType>
-class __tree_iterator;
-template <class _Tp, class _ConstNodePtr, class _DiffType>
-class __tree_const_iterator;
-
 template <class _Pointer>
 class __tree_end_node;
 template <class _VoidPtr>
@@ -68,13 +59,6 @@ class __tree_node;
 template <class _Key, class _Value>
 struct __value_type;
 
-template <class _Allocator>
-class __map_node_destructor;
-template <class _TreeIterator>
-class __map_iterator;
-template <class _TreeIterator>
-class __map_const_iterator;
-
 /*
 
 _NodePtr algorithms
@@ -492,16 +476,7 @@ _LIBCPP_HIDE_FROM_ABI void __tree_remove(_NodePtr __root, _NodePtr __z) _NOEXCEP
 // node traits
 
 template <class _Tp>
-struct __is_tree_value_type_imp : false_type {};
-
-template <class _Key, class _Value>
-struct __is_tree_value_type_imp<__value_type<_Key, _Value> > : true_type {};
-
-template <class... _Args>
-struct __is_tree_value_type : false_type {};
-
-template <class _One>
-struct __is_tree_value_type<_One> : __is_tree_value_type_imp<__remove_cvref_t<_One> > {};
+inline const bool __is_tree_value_type_v = __is_specialization_v<_Tp, __value_type>;
 
 template <class _Tp>
 struct __get_tree_key_type {
@@ -974,23 +949,23 @@ public:
     return __emplace_hint_unique_key_args(__p, __x.first, std::forward<_Pp>(__x)).first;
   }
 
-  template <class _ValueT = _Tp, __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _ValueT = _Tp, __enable_if_t<__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void
   __insert_unique_from_orphaned_node(const_iterator __p, __get_node_value_type_t<_Tp>&& __value) {
     __emplace_hint_unique(__p, const_cast<key_type&&>(__value.first), std::move(__value.second));
   }
 
-  template <class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __insert_unique_from_orphaned_node(const_iterator __p, _Tp&& __value) {
     __emplace_hint_unique(__p, std::move(__value));
   }
 
-  template <class _ValueT = _Tp, __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _ValueT = _Tp, __enable_if_t<__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __insert_multi_from_orphaned_node(const_iterator __p, value_type&& __value) {
     __emplace_hint_multi(__p, const_cast<key_type&&>(__value.first), std::move(__value.second));
   }
 
-  template <class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __insert_multi_from_orphaned_node(const_iterator __p, _Tp&& __value) {
     __emplace_hint_multi(__p, std::move(__value));
   }
@@ -1137,7 +1112,7 @@ private:
   }
   _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__tree&, false_type) _NOEXCEPT {}
 
-  template <class _From, class _ValueT = _Tp, __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _From, class _ValueT = _Tp, __enable_if_t<__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI static void __assign_value(__get_node_value_type_t<value_type>& __lhs, _From&& __rhs) {
     using __key_type = __remove_const_t<typename value_type::first_type>;
 
@@ -1147,7 +1122,7 @@ private:
     __lhs.second                         = std::forward<_From>(__rhs).second;
   }
 
-  template <class _To, class _From, class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type<_ValueT>::value, int> = 0>
+  template <class _To, class _From, class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type_v<_ValueT>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI static void __assign_value(_To& __lhs, _From&& __rhs) {
     __lhs = std::forward<_From>(__rhs);
   }

libcxx/include/__type_traits/is_specialization.h

@@ -30,15 +30,11 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 17
-
 template <class _Tp, template <class...> class _Template>
-inline constexpr bool __is_specialization_v = false; // true if and only if _Tp is a specialization of _Template
+inline const bool __is_specialization_v = false; // true if and only if _Tp is a specialization of _Template
 
 template <template <class...> class _Template, class... _Args>
-inline constexpr bool __is_specialization_v<_Template<_Args...>, _Template> = true;
-
-#endif // _LIBCPP_STD_VER >= 17
+inline const bool __is_specialization_v<_Template<_Args...>, _Template> = true;
 
 _LIBCPP_END_NAMESPACE_STD