Implement LWG 2360: 'reverse_iterator::operator*() is unimplementable'. Note that this is a (small) behavior change in the library. Reverse iterators whose base iterators' operator* return references to 'within themselves' have been sacrificed to the greater goal of avoiding data races.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@203587 91177308-0d34-0410-b5e6-96231b3b80d8

include/iterator

@@ -536,8 +536,6 @@ class _LIBCPP_TYPE_VIS_ONLY reverse_iterator
                       typename iterator_traits<_Iter>::pointer,
                       typename iterator_traits<_Iter>::reference>
 {
-private:
-    mutable _Iter __t;
 protected:
     _Iter current;
 public:
@@ -547,11 +545,11 @@ public:
     typedef typename iterator_traits<_Iter>::pointer         pointer;
 
     _LIBCPP_INLINE_VISIBILITY reverse_iterator() : current() {}
-    _LIBCPP_INLINE_VISIBILITY explicit reverse_iterator(_Iter __x) : __t(__x), current(__x) {}
+    _LIBCPP_INLINE_VISIBILITY explicit reverse_iterator(_Iter __x) : current(__x) {}
     template <class _Up> _LIBCPP_INLINE_VISIBILITY reverse_iterator(const reverse_iterator<_Up>& __u)
-        : __t(__u.base()), current(__u.base()) {}
+        : current(__u.base()) {}
     _LIBCPP_INLINE_VISIBILITY _Iter base() const {return current;}
-    _LIBCPP_INLINE_VISIBILITY reference operator*() const {__t = current; return *--__t;}
+    _LIBCPP_INLINE_VISIBILITY reference operator*() const {_Iter __tmp = current; return *--__tmp;}
     _LIBCPP_INLINE_VISIBILITY pointer  operator->() const {return _VSTD::addressof(operator*());}
     _LIBCPP_INLINE_VISIBILITY reverse_iterator& operator++() {--current; return *this;}
     _LIBCPP_INLINE_VISIBILITY reverse_iterator  operator++(int)

test/iterators/predef.iterators/reverse.iterators/reverse.iter.ops/reverse.iter.op.star/op_star.pass.cpp

@@ -15,6 +15,8 @@
 
 // Be sure to respect LWG 198:
 //    http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#198
+// LWG 198 was superseded by LWG 2360
+//    http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2360
 
 #include <iterator>
 #include <cassert>
@@ -30,26 +32,6 @@ public:
         {return x.data_ == y.data_;}
 };
 
-template <class It>
-class weird_iterator
-{
-    It it_;
-public:
-    typedef It                              value_type;
-    typedef std::bidirectional_iterator_tag iterator_category;
-    typedef std::ptrdiff_t                  difference_type;
-    typedef It*                             pointer;
-    typedef It&                             reference;
-
-    weird_iterator() {}
-    explicit weird_iterator(It it) : it_(it) {}
-    ~weird_iterator() {it_ = It();}
-
-    reference operator*() {return it_;}
-
-    weird_iterator& operator--() {return *this;}
-};
-
 template <class It>
 void
 test(It i, typename std::iterator_traits<It>::value_type x)
@@ -60,7 +42,6 @@ test(It i, typename std::iterator_traits<It>::value_type x)
 
 int main()
 {
-    test(weird_iterator<A>(A()), A());
     A a;
     test(&a+1, A());
 }

test/iterators/predef.iterators/reverse.iterators/reverse.iter.ops/reverse.iter.opref/op_arrow.pass.cpp

@@ -15,6 +15,9 @@
 
 // Be sure to respect LWG 198:
 //    http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#198
+// LWG 198 was superseded by LWG 2360
+//    http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2360
+
 
 #include <iterator>
 #include <list>
@@ -33,27 +36,6 @@ public:
         {return x.data_ == y.data_;}
 };
 
-template <class It>
-class weird_iterator
-{
-    It it_;
-public:
-    typedef It                              value_type;
-    typedef std::bidirectional_iterator_tag iterator_category;
-    typedef std::ptrdiff_t                  difference_type;
-    typedef It*                             pointer;
-    typedef It&                             reference;
-
-    weird_iterator() {}
-    explicit weird_iterator(It it) : it_(it) {}
-    ~weird_iterator() {it_ = It();}
-
-    reference operator*() {return it_;}
-    pointer operator->() {return &it_;}
-
-    weird_iterator& operator--() {return *this;}
-};
-
 template <class It>
 void
 test(It i, typename std::iterator_traits<It>::value_type x)
@@ -79,7 +61,6 @@ public:
 
 int main()
 {
-    test(weird_iterator<A>(A()), A());
     A a;
     test(&a+1, A());
     

www/cxx1y_status.html

@@ -265,7 +265,7 @@
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2356">2356</a></td><td>Stability of erasure in unordered associative containers</td><td>Issaquah</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2357">2357</a></td><td>Remaining "Assignable" requirement</td><td>Issaquah</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2359">2359</a></td><td>How does regex_constants::nosubs affect basic_regex::mark_count()?</td><td>Issaquah</td><td>Complete</td></tr>
-	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2360">2360</a></td><td>reverse_iterator::operator*() is unimplementable</td><td>Issaquah</td><td></td></tr>
+	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2360">2360</a></td><td>reverse_iterator::operator*() is unimplementable</td><td>Issaquah</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2104">2104</a></td><td>unique_lock move-assignment should not be noexcept</td><td>Issaquah</td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2186">2186</a></td><td>Incomplete action on async/launch::deferred</td><td>Issaquah</td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2075">2075</a></td><td>Progress guarantees, lock-free property, and scheduling assumptions</td><td>Issaquah</td><td></td></tr>