fix some comments

Author: huixie90

libcxx/include/__flat_set/flat_set.h

@@ -38,6 +38,7 @@
 #include <__iterator/next.h>
 #include <__iterator/ranges_iterator_traits.h>
 #include <__iterator/reverse_iterator.h>
+#include <__iterator/prev.h>
 #include <__memory/allocator_traits.h>
 #include <__memory/uses_allocator.h>
 #include <__memory/uses_allocator_construction.h>
@@ -359,9 +360,9 @@ class flat_set {
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> emplace(_Args&&... __args) {
     if constexpr (sizeof...(__args) == 1 && (is_same_v<remove_cvref_t<_Args>, _Key> && ...)) {
-      return __try_emplace(std::forward<_Args>(__args)...);
+      return __emplace(std::forward<_Args>(__args)...);
     } else {
-      return __try_emplace(_Key(std::forward<_Args>(__args)...));
+      return __emplace(_Key(std::forward<_Args>(__args)...));
     }
   }
 
@@ -688,7 +689,7 @@ class flat_set {
   }
 
   template <class _Kp>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __try_emplace(_Kp&& __key) {
+  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace(_Kp&& __key) {
     auto __it = lower_bound(__key);
     if (__it == end() || __compare_(__key, *__it)) {
       return pair<iterator, bool>(__emplace_exact_pos(__it, std::forward<_Kp>(__key)), true);
@@ -699,7 +700,7 @@ class flat_set {
 
   template <class _Kp>
   _LIBCPP_HIDE_FROM_ABI bool __is_hint_correct(const_iterator __hint, _Kp&& __key) {
-    if (__hint != cbegin() && !__compare_(*(__hint - 1), __key)) {
+    if (__hint != cbegin() && !__compare_(*std::prev(__hint), __key)) {
       return false;
     }
     if (__hint != cend() && __compare_(*__hint, __key)) {
@@ -714,11 +715,11 @@ class flat_set {
       if (__hint == cend() || __compare_(__key, *__hint)) {
         return __emplace_exact_pos(__hint, std::forward<_Kp>(__key));
       } else {
-        // key equals
+        // we already have an equal key
         return __hint;
       }
     } else {
-      return __try_emplace(std::forward<_Kp>(__key)).first;
+      return __emplace(std::forward<_Kp>(__key)).first;
     }
   }
 

libcxx/include/__flat_set/ra_iterator.h

@@ -16,6 +16,7 @@
 #include <__iterator/iterator_traits.h>
 #include <__type_traits/is_constructible.h>
 #include <__utility/move.h>
+#include <iterator>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -31,7 +32,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 /**
  * __ra_iterator is a random access iterator that wraps an underlying iterator.
  * It also stores the underlying container type in its type so that algorithms
- * can optimize based on the underlying container type.
+ * can optimize based on the underlying container type, and to avoid inadvertently
+ * mixing iterators coming from different containers..
  */
 template <class _Container, class _Iterator>
 struct __ra_iterator {
@@ -40,6 +42,8 @@ struct __ra_iterator {
 
   friend _Container;
 
+  static_assert(std::random_access_iterator<_Iterator>, "Underlying iterator must be a random access iterator");
+
 public:
   using iterator_concept  = random_access_iterator_tag; // deliberately lower contiguous_iterator
   using iterator_category = random_access_iterator_tag;
@@ -50,92 +54,94 @@ struct __ra_iterator {
     requires is_default_constructible_v<_Iterator>
   = default;
 
-  _LIBCPP_HIDE_FROM_ABI explicit __ra_iterator(_Iterator __iter) : __iter_(std::move(__iter)) {}
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr __ra_iterator(_Iterator __iter) : __iter_(std::move(__iter)) {}
 
-  _LIBCPP_HIDE_FROM_ABI _Iterator __base() const noexcept(noexcept(_Iterator(__iter_))) { return __iter_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __base() const noexcept(noexcept(_Iterator(__iter_))) { return __iter_; }
 
-  _LIBCPP_HIDE_FROM_ABI decltype(auto) operator*() const { return *__iter_; }
-  _LIBCPP_HIDE_FROM_ABI decltype(auto) operator->() const
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const { return *__iter_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator->() const
     requires requires { __iter_.operator->(); }
   {
     return __iter_.operator->();
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator++() {
     ++__iter_;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator operator++(int) {
     __ra_iterator __tmp(*this);
     ++*this;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator--() {
     --__iter_;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator operator--(int) {
     __ra_iterator __tmp(*this);
     --*this;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator& operator+=(difference_type __x) {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator+=(difference_type __x) {
     __iter_ += __x;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __ra_iterator& operator-=(difference_type __x) {
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator-=(difference_type __x) {
     __iter_ -= __x;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI decltype(auto) operator[](difference_type __n) const { return *(*this + __n); }
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type __n) const { return *(*this + __n); }
 
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __ra_iterator& __x, const __ra_iterator& __y) {
     return __x.__iter_ == __y.__iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator<(const __ra_iterator& __x, const __ra_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<(const __ra_iterator& __x, const __ra_iterator& __y) {
     return __x.__iter_ < __y.__iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator>(const __ra_iterator& __x, const __ra_iterator& __y) { return __y < __x; }
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return __y < __x;
+  }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator<=(const __ra_iterator& __x, const __ra_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<=(const __ra_iterator& __x, const __ra_iterator& __y) {
     return !(__y < __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator>=(const __ra_iterator& __x, const __ra_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>=(const __ra_iterator& __x, const __ra_iterator& __y) {
     return !(__x < __y);
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend auto operator<=>(const __ra_iterator& __x, const __ra_iterator& __y)
+  _LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(const __ra_iterator& __x, const __ra_iterator& __y)
     requires three_way_comparable<_Iterator>
   {
     return __x.__iter_ <=> __y.__iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __ra_iterator operator+(const __ra_iterator& __i, difference_type __n) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr __ra_iterator operator+(const __ra_iterator& __i, difference_type __n) {
     auto __tmp = __i;
     __tmp += __n;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __ra_iterator operator+(difference_type __n, const __ra_iterator& __i) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr __ra_iterator operator+(difference_type __n, const __ra_iterator& __i) {
     return __i + __n;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __ra_iterator operator-(const __ra_iterator& __i, difference_type __n) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr __ra_iterator operator-(const __ra_iterator& __i, difference_type __n) {
     auto __tmp = __i;
     __tmp -= __n;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend difference_type operator-(const __ra_iterator& __x, const __ra_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __ra_iterator& __x, const __ra_iterator& __y) {
     return __x.__iter_ - __y.__iter_;
   }
 };