[libcxx-commits] [PATCH] D110198: [libc++] Fix __wrap_iter to be a proper contiguous iterator.

[Arthur O'Dwyer via Phabricator via libcxx-commits]

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//The latest installment in the ever-evolving saga of `__cpp17_contiguous_iterator`, `__wrap_iter`, and `__unwrap_iter`...//

Instead of overloading `__to_address`, let's specialize `pointer_traits`. Function overloads need to be in scope at the point where they're called, whereas template specializations do not. (User code can provide pointer_traits specializations to be used by already-included library code, so obviously `__wrap_iter` can do the same.)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110198

Files:
  libcxx/include/__iterator/wrap_iter.h
  libcxx/test/std/utilities/memory/pointer.conversion/to_address_std_iterators.pass.cpp


Index: libcxx/test/std/utilities/memory/pointer.conversion/to_address_std_iterators.pass.cpp
===================================================================
--- libcxx/test/std/utilities/memory/pointer.conversion/to_address_std_iterators.pass.cpp
+++ libcxx/test/std/utilities/memory/pointer.conversion/to_address_std_iterators.pass.cpp
@@ -10,10 +10,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
-// TODO: We should enable this test in Debug mode once we fix __wrap_iter
-//       to be a proper contiguous_iterator.
-// UNSUPPORTED: LIBCXX-DEBUG-FIXME
-
 // template <class T> constexpr T* to_address(T* p) noexcept;
 // template <class Ptr> constexpr auto to_address(const Ptr& p) noexcept;
 
Index: libcxx/include/__iterator/wrap_iter.h
===================================================================
--- libcxx/include/__iterator/wrap_iter.h
+++ libcxx/include/__iterator/wrap_iter.h
@@ -13,7 +13,7 @@
 #include <__config>
 #include <__debug>
 #include <__iterator/iterator_traits.h>
-#include <__memory/pointer_traits.h> // __to_address
+#include <__memory/pointer_traits.h>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -283,12 +283,33 @@
 struct __is_cpp17_contiguous_iterator<__wrap_iter<_It> > : true_type {};
 #endif
 
-template <class _Iter>
-_LIBCPP_CONSTEXPR
-decltype(_VSTD::__to_address(declval<_Iter>()))
-__to_address(__wrap_iter<_Iter> __w) _NOEXCEPT {
-    return _VSTD::__to_address(__w.base());
-}
+template <class _It>
+struct _LIBCPP_TEMPLATE_VIS pointer_traits<__wrap_iter<_It> >
+{
+    typedef __wrap_iter<_It> pointer;
+    typedef typename pointer_traits<_It>::element_type element_type;
+    typedef typename pointer_traits<_It>::difference_type difference_type;
+
+#ifndef _LIBCPP_CXX03_LANG
+    template <class _Up> using rebind = _Up*;
+#else
+    template <class _Up> struct rebind {typedef _Up* other;};
+#endif
+
+private:
+    struct __nat {};
+public:
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    static element_type *to_address(pointer __w) _NOEXCEPT {
+        return _VSTD::__to_address(__w.base());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    static pointer pointer_to(typename conditional<is_void<element_type>::value,
+                                      __nat, element_type>::type& __r) _NOEXCEPT {
+        return pointer_traits<_It>::pointer_to(__r);
+    }
+};
 
 _LIBCPP_END_NAMESPACE_STD
 


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