Revert to libc++ pointer_traits::pointer_to with necessary cast

Author: winner245

libcxx/include/forward_list

@@ -300,16 +300,8 @@ struct __forward_node_traits {
     return __p;
   }
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI static __begin_node_pointer __as_iter_node(__node_pointer __p) {
-#  ifdef _LIBCPP_CXX03_LANG
-    return static_cast<__begin_node_pointer>(__p);
-#  else
-    if constexpr (std::is_pointer<__begin_node_pointer>::value) {
-      return static_cast<__begin_node_pointer>(__p);
-    } else {
-      return __p ? __begin_node_pointer::pointer_to(*static_cast<__begin_node*>(std::addressof(*__p)))
-                 : static_cast<__begin_node_pointer>(nullptr);
-    }
-#  endif
+    return __p ? pointer_traits<__begin_node_pointer>::pointer_to(*static_cast<__begin_node*>(std::addressof(*__p)))
+               : static_cast<__begin_node_pointer>(nullptr);
   }
 };
 
@@ -324,16 +316,9 @@ struct __forward_begin_node {
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI explicit __forward_begin_node(pointer __n) : __next_(__n) {}
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __begin_node_pointer __next_as_begin() const {
-#  ifdef _LIBCPP_CXX03_LANG
-    return static_cast<__begin_node_pointer>(__next_);
-#  else
-    if constexpr (std::is_pointer<__begin_node_pointer>::value) {
-      return static_cast<__begin_node_pointer>(__next_);
-    } else {
-      return __next_ ? __begin_node_pointer::pointer_to(*static_cast<__forward_begin_node*>(std::addressof(*__next_)))
-                     : static_cast<__begin_node_pointer>(nullptr);
-    }
-#  endif
+    return __next_ ? pointer_traits<__begin_node_pointer>::pointer_to(
+                         *static_cast<__forward_begin_node*>(std::addressof(*__next_)))
+                   : static_cast<__begin_node_pointer>(nullptr);
   }
 };
 
@@ -389,17 +374,8 @@ class _LIBCPP_TEMPLATE_VIS __forward_list_iterator {
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __begin_node_pointer __get_begin() const { return __ptr_; }
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __node_pointer __get_unsafe_node_pointer() const {
-#  ifdef _LIBCPP_CXX03_LANG
-    return static_cast<__node_pointer>(__ptr_);
-#  else
-    if constexpr (std::is_pointer<__node_pointer>::value) {
-      return static_cast<__node_pointer>(__ptr_);
-    } else {
-      return __ptr_ ? __node_pointer::pointer_to(
-                          *static_cast<__node_type*>(const_cast<__begin_node_type*>(std::addressof(*__ptr_))))
-                    : static_cast<__node_pointer>(nullptr);
-    }
-#  endif
+    return __ptr_ ? pointer_traits<__node_pointer>::pointer_to(*static_cast<__node_type*>(std::addressof(*__ptr_)))
+                  : static_cast<__node_pointer>(nullptr);
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI explicit __forward_list_iterator(nullptr_t) _NOEXCEPT
@@ -469,17 +445,8 @@ class _LIBCPP_TEMPLATE_VIS __forward_list_const_iterator {
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __begin_node_pointer __get_begin() const { return __ptr_; }
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __node_pointer __get_unsafe_node_pointer() const {
-#  ifdef _LIBCPP_CXX03_LANG
-    return static_cast<__node_pointer>(__ptr_);
-#  else
-    if constexpr (std::is_pointer<__node_pointer>::value) {
-      return static_cast<__node_pointer>(__ptr_);
-    } else {
-      return __ptr_ ? __node_pointer::pointer_to(
-                          *static_cast<__node_type*>(const_cast<__begin_node_type*>(std::addressof(*__ptr_))))
-                    : static_cast<__node_pointer>(nullptr);
-    }
-#  endif
+    return __ptr_ ? pointer_traits<__node_pointer>::pointer_to(*static_cast<__node_type*>(std::addressof(*__ptr_)))
+                  : static_cast<__node_pointer>(nullptr);
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI explicit __forward_list_const_iterator(nullptr_t) _NOEXCEPT
@@ -553,27 +520,12 @@ protected:
   _LIBCPP_COMPRESSED_PAIR(__begin_node, __before_begin_, __node_allocator, __alloc_);
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __begin_node_pointer __before_begin() _NOEXCEPT {
-#  ifdef _LIBCPP_CXX03_LANG
     return pointer_traits<__begin_node_pointer>::pointer_to(__before_begin_);
-#  else
-    if constexpr (std::is_pointer<__begin_node_pointer>::value) {
-      return std::addressof(__before_begin_);
-    } else {
-      return __begin_node_pointer::pointer_to(*std::addressof(__before_begin_));
-    }
-#  endif
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __begin_node_pointer __before_begin() const _NOEXCEPT {
-#  ifdef _LIBCPP_CXX03_LANG
-    return pointer_traits<__begin_node_pointer>::pointer_to(const_cast<__begin_node&>(__before_begin_));
-#  else
-    if constexpr (std::is_pointer<__begin_node_pointer>::value) {
-      return const_cast<__begin_node*>(std::addressof(__before_begin_));
-    } else {
-      return __begin_node_pointer::pointer_to(*const_cast<__begin_node*>(std::addressof(__before_begin_)));
-    }
-#  endif
+    return pointer_traits<__begin_node_pointer>::pointer_to(
+        *const_cast<__begin_node*>(std::addressof(__before_begin_)));
   }
 
   typedef __forward_list_iterator<__node_pointer> iterator;