[libc++] Add C++20 contiguous_iterator_tag.
This work is part of an ongoing effort to allow libc++ to
optimize user provided contiguous iterators.
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 45d048c20440989df2b4e1be1f9343225e7741ab
diff --git a/include/iterator b/include/iterator
index c5c0f66..6a9a082 100644
--- a/include/iterator
+++ b/include/iterator
@@ -440,6 +440,11 @@
struct _LIBCPP_TEMPLATE_VIS forward_iterator_tag : public input_iterator_tag {};
struct _LIBCPP_TEMPLATE_VIS bidirectional_iterator_tag : public forward_iterator_tag {};
struct _LIBCPP_TEMPLATE_VIS random_access_iterator_tag : public bidirectional_iterator_tag {};
+#if _LIBCPP_STD_VER > 17
+// TODO(EricWF) contiguous_iterator_tag is provided as an extension prior to
+// C++20 to allow optimizations for users providing wrapped iterator types.
+struct _LIBCPP_TEMPLATE_VIS contiguous_iterator_tag: public random_access_iterator_tag { };
+#endif
template <class _Tp>
struct __has_iterator_typedefs
@@ -510,6 +515,9 @@
typedef _Tp* pointer;
typedef _Tp& reference;
typedef random_access_iterator_tag iterator_category;
+#if _LIBCPP_STD_VER > 17
+ typedef contiguous_iterator_tag iterator_concept;
+#endif
};
template <class _Tp, class _Up, bool = __has_iterator_category<iterator_traits<_Tp> >::value>
@@ -532,6 +540,11 @@
template <class _Tp>
struct __is_random_access_iterator : public __has_iterator_category_convertible_to<_Tp, random_access_iterator_tag> {};
+#if _LIBCPP_STD_VER > 17
+template <class _Tp>
+struct __is_contiguous_iterator : public __has_iterator_category_convertible_to<_Tp, contiguous_iterator_tag> {};
+#endif
+
template <class _Tp>
struct __is_exactly_input_iterator
: public integral_constant<bool,