constexpr array support C++1z (P0031)

[lefticus]

Summary

• array constexpr-ized
• associated iterator functions constexpr-ized
• unit tests added for array
• unit tests added for iterator

Unit tests for std::array required non-const constexpr context for tests, so constexpr helper functions were added in unit tests, with static_assert calls on resulting values.

Ref: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0031r0.html

[mclow.lists]

All look fine to me - but needs tests.

[lefticus]

• Updated title and summary to be more accurate.
• Implemented tests for constexpr std::array access.
• Added required constexpr iterator support.
• Implemented tests for constexpr iterator functions

[EricWF]

For the most part this LGTM. Thanks for putting in all this work. I've noted some places where the test coverage could be improved.

include/array

156

This is untested.

160

This is untested.

165

Untested.

169

Untested.

208

Untested.

include/iterator

527

Untested.

536

Untested.

565

Untested.

1132

This is a C++03 only branch, but I guess it's more consistent to apply the macro.

test/std/containers/sequences/array/indexing.pass.cpp

41

Missing conditional directive terminator.

86

C doesn't name a type.

test/std/containers/sequences/array/iterators.pass.cpp

113

Include test_macros.h and use TEST_STD_VER please.

[lefticus]

Fixed syntax errors in test files.

[lefticus]

I believe I messed up the context for the files, will attempt to resubmit the patch.

[lefticus]

Correct context from last patch

[lefticus]

I believe all or most of the "untested" comments are correctly tested in the updated test files via static_asserts with contexpr. I've commented on just the first one to make sure I understand correctly.

include/array

156

This should be tested in begin.pass.cpp:28 correct?

[mclow.lists]

This diff no longer applies cleanly, and I've added some formatting concerns. However, the content looks fine to me.

include/array

176

Nit: I would put the _LIBCPP_CONSTEXPR_AFTER_CXX14 on the same line as _LIBCPP_INLINE_VISIBILITY to keep the lines from getting too long.

190–191

And break this line after the macros for the same reason as L#176

include/iterator

526

Here, I would smoosh them all together on the same line: inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14

[lefticus]

Address formatting concerns and out-of-date-ness of patch relative to trunk/master

[mclow.lists]

Other than the iterator.primitives/iterator.operations/prev.pass.cpp test, I think this is good to go.

test/std/iterators/iterator.primitives/iterator.operations/prev.pass.cpp

47

Won't this fail on C++11 (i.e, doesn't it need a #if TEST_STD_VER > 14)?

[lefticus]

Add C++1z check around constexpr tests, based on mclow's feedback

[EricWF]

@lefticus Are you still interested in working on this? If so could you please split the changes for array into a separate patch? Marshall seems to have implemented some of the changes in <iterator> and that's causing merge conflicts.

[lefticus]

@EricWF I have too many other things going on right now to be able to look at it for at least the next few months.

[EricWF]

Looks like @mclow.lists just committed another version of this paper, so this patch is no longer needed.

Resigning as reviewer.

include/array

struct array
     typedef std::reverse_iterator<iterator> reverse_iterator;
     typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
     // No explicit construct/copy/destroy for aggregate type
     void fill(const T& u);
     void swap(array& a) noexcept(is_nothrow_swappable_v<T>);
 
     // iterators:
-    iterator begin() noexcept;
-    const_iterator begin() const noexcept;
-    iterator end() noexcept;
-    const_iterator end() const noexcept;
-
-    reverse_iterator rbegin() noexcept;
-    const_reverse_iterator rbegin() const noexcept;
-    reverse_iterator rend() noexcept;
-    const_reverse_iterator rend() const noexcept;
-
-    const_iterator cbegin() const noexcept;
-    const_iterator cend() const noexcept;
-    const_reverse_iterator crbegin() const noexcept;
-    const_reverse_iterator crend() const noexcept;
+    iterator begin() noexcept; // constexpr in C++17
+    const_iterator begin() const noexcept; // constexpr in C++17
+    iterator end() noexcept; // constexpr in C++17
+    const_iterator end() const noexcept; // constexpr in C++17
+
+    reverse_iterator rbegin() noexcept; // constexpr in C++17
+    const_reverse_iterator rbegin() const noexcept; // constexpr in C++17
+    reverse_iterator rend() noexcept; // constexpr in C++17
+    const_reverse_iterator rend() const noexcept; // constexpr in C++17
+
+    const_iterator cbegin() const noexcept; // constexpr in C++17
+    const_iterator cend() const noexcept; // constexpr in C++17
+    const_reverse_iterator crbegin() const noexcept; // constexpr in C++17
+    const_reverse_iterator crend() const noexcept; // constexpr in C++17
 
     // capacity:
     constexpr size_type size() const noexcept;
     constexpr size_type max_size() const noexcept;
     constexpr bool empty() const noexcept;
 
     // element access:
-    reference operator[](size_type n);
+    reference operator[](size_type n); // constexpr in C++17
     const_reference operator[](size_type n) const; // constexpr in C++14
     const_reference at(size_type n) const; // constexpr in C++14
-    reference at(size_type n);
+    reference at(size_type n); // constexpr in C++17
 
-    reference front();
+    reference front(); // constexpr in C++17
     const_reference front() const; // constexpr in C++14
-    reference back();
+    reference back(); // constexpr in C++17
     const_reference back() const; // constexpr in C++14
 
-    T* data() noexcept;
-    const T* data() const noexcept;
+    T* data() noexcept; // constexpr in C++17
+    const T* data() const noexcept; // constexpr in C++17
 };
 
 template <class T, size_t N>
   bool operator==(const array<T,N>& x, const array<T,N>& y);
 template <class T, size_t N>
   bool operator!=(const array<T,N>& x, const array<T,N>& y);
 template <class T, size_t N>
   bool operator<(const array<T,N>& x, const array<T,N>& y);
struct _LIBCPP_TYPE_VIS_ONLY array
     _LIBCPP_INLINE_VISIBILITY
     void __swap_dispatch(std::true_type, array&) {}
 
     _LIBCPP_INLINE_VISIBILITY
     void __swap_dispatch(std::false_type, array& __a)
         { _VSTD::swap_ranges(__elems_, __elems_ + _Size, __a.__elems_);}
 
     // iterators:
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     iterator begin() _NOEXCEPT {return iterator(__elems_);}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_iterator begin() const _NOEXCEPT {return const_iterator(__elems_);}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     iterator end() _NOEXCEPT {return iterator(__elems_ + _Size);}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_iterator end() const _NOEXCEPT {return const_iterator(__elems_ + _Size);}
 
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     reverse_iterator rbegin() _NOEXCEPT {return reverse_iterator(end());}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_reverse_iterator rbegin() const _NOEXCEPT {return const_reverse_iterator(end());}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     reverse_iterator rend() _NOEXCEPT {return reverse_iterator(begin());}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_reverse_iterator rend() const _NOEXCEPT {return const_reverse_iterator(begin());}
 
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_iterator cbegin() const _NOEXCEPT {return begin();}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_iterator cend() const _NOEXCEPT {return end();}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_reverse_iterator crbegin() const _NOEXCEPT {return rbegin();}
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
     const_reverse_iterator crend() const _NOEXCEPT {return rend();}
 
     // capacity:
     _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR size_type size() const _NOEXCEPT {return _Size;}
     _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR size_type max_size() const _NOEXCEPT {return _Size;}
     _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR bool empty() const _NOEXCEPT {return _Size == 0;}
 
     // element access:
-    _LIBCPP_INLINE_VISIBILITY reference operator[](size_type __n)             {return __elems_[__n];}
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const_reference operator[](size_type __n) const {return __elems_[__n];}
-    reference at(size_type __n);
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
+    reference operator[](size_type __n)             {return __elems_[__n];}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 
+    const_reference operator[](size_type __n) const {return __elems_[__n];}
+    _LIBCPP_CONSTEXPR_AFTER_CXX14 reference at(size_type __n);
     _LIBCPP_CONSTEXPR_AFTER_CXX11 const_reference at(size_type __n) const;
 
-    _LIBCPP_INLINE_VISIBILITY reference front()             {return __elems_[0];}
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const_reference front() const {return __elems_[0];}
-    _LIBCPP_INLINE_VISIBILITY reference back()              {return __elems_[_Size > 0 ? _Size-1 : 0];}
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const_reference back() const  {return __elems_[_Size > 0 ? _Size-1 : 0];}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
+    reference front()             {return __elems_[0];}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 
+    const_reference front() const {return __elems_[0];}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
+    reference back()              {return __elems_[_Size > 0 ? _Size-1 : 0];}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 
+    const_reference back() const  {return __elems_[_Size > 0 ? _Size-1 : 0];}
 
     _LIBCPP_INLINE_VISIBILITY
-    value_type* data() _NOEXCEPT {return __elems_;}
+    _LIBCPP_CONSTEXPR_AFTER_CXX14 value_type* data() _NOEXCEPT {return __elems_;}
     _LIBCPP_INLINE_VISIBILITY
-    const value_type* data() const _NOEXCEPT {return __elems_;}
+    _LIBCPP_CONSTEXPR_AFTER_CXX14 const value_type* data() const _NOEXCEPT {return __elems_;}
 };
 
 template <class _Tp, size_t _Size>
+_LIBCPP_CONSTEXPR_AFTER_CXX14
 typename array<_Tp, _Size>::reference
 array<_Tp, _Size>::at(size_type __n)
 {
     if (__n >= _Size)
 #ifndef _LIBCPP_NO_EXCEPTIONS
         throw out_of_range("array::at");
 #else
         assert(!"array::at out_of_range");

include/iterator

public:
     ostreambuf_iterator(streambuf_type* s) noexcept;
     ostreambuf_iterator& operator=(charT c);
     ostreambuf_iterator& operator*();
     ostreambuf_iterator& operator++();
     ostreambuf_iterator& operator++(int);
     bool failed() const noexcept;
 };
 
-template <class C> auto begin(C& c) -> decltype(c.begin());
-template <class C> auto begin(const C& c) -> decltype(c.begin());
-template <class C> auto end(C& c) -> decltype(c.end());
-template <class C> auto end(const C& c) -> decltype(c.end());
-template <class T, size_t N> T* begin(T (&array)[N]);
-template <class T, size_t N> T* end(T (&array)[N]);
-
-template <class C> auto cbegin(const C& c) -> decltype(std::begin(c));        // C++14
-template <class C> auto cend(const C& c) -> decltype(std::end(c));            // C++14
-template <class C> auto rbegin(C& c) -> decltype(c.rbegin());                 // C++14
-template <class C> auto rbegin(const C& c) -> decltype(c.rbegin());           // C++14
-template <class C> auto rend(C& c) -> decltype(c.rend());                     // C++14
-template <class C> auto rend(const C& c) -> decltype(c.rend());               // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto begin(C& c) -> decltype(c.begin());
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto begin(const C& c) -> decltype(c.begin());
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto end(C& c) -> decltype(c.end());
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto end(const C& c) -> decltype(c.end());
+template <class T, size_t N> _LIBCPP_CONSTEXPR_AFTER_CXX14 T* begin(T (&array)[N]);
+template <class T, size_t N> _LIBCPP_CONSTEXPR_AFTER_CXX14 T* end(T (&array)[N]);
+
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto cbegin(const C& c) -> decltype(std::begin(c));        // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto cend(const C& c) -> decltype(std::end(c));            // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto rbegin(C& c) -> decltype(c.rbegin());                 // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto rbegin(const C& c) -> decltype(c.rbegin());           // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto rend(C& c) -> decltype(c.rend());                     // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto rend(const C& c) -> decltype(c.rend());               // C++14
 template <class E> reverse_iterator<const E*> rbegin(initializer_list<E> il); // C++14
 template <class E> reverse_iterator<const E*> rend(initializer_list<E> il);   // C++14
-template <class T, size_t N> reverse_iterator<T*> rbegin(T (&array)[N]);      // C++14
-template <class T, size_t N> reverse_iterator<T*> rend(T (&array)[N]);        // C++14
-template <class C> auto crbegin(const C& c) -> decltype(std::rbegin(c));      // C++14
-template <class C> auto crend(const C& c) -> decltype(std::rend(c));          // C++14
+template <class T, size_t N> _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator<T*> rbegin(T (&array)[N]);      // C++14
+template <class T, size_t N> _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator<T*> rend(T (&array)[N]);        // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto crbegin(const C& c) -> decltype(std::rbegin(c));      // C++14
+template <class C> _LIBCPP_CONSTEXPR_AFTER_CXX14 auto crend(const C& c) -> decltype(std::rend(c));          // C++14
 
 // 24.8, container access:
 template <class C> constexpr auto size(const C& c) -> decltype(c.size());         // C++17
 template <class T, size_t N> constexpr size_t size(const T (&array)[N]) noexcept; // C++17
 template <class C> constexpr auto empty(const C& c) -> decltype(c.empty());       // C++17
 template <class T, size_t N> constexpr bool empty(const T (&array)[N]) noexcept;  // C++17
 template <class E> constexpr bool empty(initializer_list<E> il) noexcept;         // C++17
 template <class C> constexpr auto data(C& c) -> decltype(c.data());               // C++17
struct _LIBCPP_TYPE_VIS_ONLY iterator
     typedef _Tp        value_type;
     typedef _Distance  difference_type;
     typedef _Pointer   pointer;
     typedef _Reference reference;
     typedef _Category  iterator_category;
 };
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 void __advance(_InputIter& __i,
              typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag)
 {
     for (; __n > 0; --__n)
         ++__i;
 }
 
 template <class _BiDirIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 void __advance(_BiDirIter& __i,
              typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag)
 {
     if (__n >= 0)
         for (; __n > 0; --__n)
             ++__i;
     else
         for (; __n < 0; ++__n)
             --__i;
 }
 
 template <class _RandIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 void __advance(_RandIter& __i,
              typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag)
 {
    __i += __n;
 }
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 void advance(_InputIter& __i,
              typename iterator_traits<_InputIter>::difference_type __n)
 {
     __advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category());
 }
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename iterator_traits<_InputIter>::difference_type
 __distance(_InputIter __first, _InputIter __last, input_iterator_tag)
 {
     typename iterator_traits<_InputIter>::difference_type __r(0);
     for (; __first != __last; ++__first)
         ++__r;
     return __r;
 }
 
 template <class _RandIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename iterator_traits<_RandIter>::difference_type
 __distance(_RandIter __first, _RandIter __last, random_access_iterator_tag)
 {
     return __last - __first;
 }
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename iterator_traits<_InputIter>::difference_type
 distance(_InputIter __first, _InputIter __last)
 {
     return __distance(__first, __last, typename iterator_traits<_InputIter>::iterator_category());
 }
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 _InputIter
 next(_InputIter __x,
      typename iterator_traits<_InputIter>::difference_type __n = 1,
      typename enable_if<__is_input_iterator<_InputIter>::value>::type* = 0)
 {
     _VSTD::advance(__x, __n);
     return __x;
 }
 
 template <class _BidiretionalIter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 _BidiretionalIter
 prev(_BidiretionalIter __x,
      typename iterator_traits<_BidiretionalIter>::difference_type __n = 1,
      typename enable_if<__is_bidirectional_iterator<_BidiretionalIter>::value>::type* = 0)
 {
     _VSTD::advance(__x, -__n);
     return __x;
 }

 protected:
     _Iter current;
 public:
     typedef _Iter                                            iterator_type;
     typedef typename iterator_traits<_Iter>::difference_type difference_type;
     typedef typename iterator_traits<_Iter>::reference       reference;
     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) {}
-    template <class _Up> _LIBCPP_INLINE_VISIBILITY reverse_iterator(const reverse_iterator<_Up>& __u)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator() : current() {}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 explicit reverse_iterator(_Iter __x) : __t(__x), current(__x) {}
+    template <class _Up> _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator(const reverse_iterator<_Up>& __u)
         : __t(__u.base()), current(__u.base()) {}
-    _LIBCPP_INLINE_VISIBILITY _Iter base() const {return current;}
-    _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)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 _Iter base() const {return current;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reference operator*() const {_Iter __tmp = current; return *--__tmp;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 pointer  operator->() const {return _VSTD::addressof(operator*());}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator& operator++() {--current; return *this;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator  operator++(int)
         {reverse_iterator __tmp(*this); --current; return __tmp;}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator& operator--() {++current; return *this;}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator  operator--(int)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator& operator--() {++current; return *this;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator  operator--(int)
         {reverse_iterator __tmp(*this); ++current; return __tmp;}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator  operator+ (difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator  operator+ (difference_type __n) const
         {return reverse_iterator(current - __n);}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator& operator+=(difference_type __n)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator& operator+=(difference_type __n)
         {current -= __n; return *this;}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator  operator- (difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator  operator- (difference_type __n) const
         {return reverse_iterator(current + __n);}
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator& operator-=(difference_type __n)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reverse_iterator& operator-=(difference_type __n)
         {current += __n; return *this;}
-    _LIBCPP_INLINE_VISIBILITY reference         operator[](difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reference         operator[](difference_type __n) const
         {return *(*this + __n);}
 };
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator==(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() == __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator<(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() > __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator!=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() != __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() < __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator>=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() <= __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator<=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __x.base() >= __y.base();
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 auto
 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 -> decltype(__y.base() - __x.base())
 {
     return __y.base() - __x.base();
 }
 #else
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 typename reverse_iterator<_Iter1>::difference_type
 operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
 {
     return __y.base() - __x.base();
 }
 #endif
 
 template <class _Iter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 reverse_iterator<_Iter>
 operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x)
 {
     return reverse_iterator<_Iter>(__x.base() - __n);
 }
 
 #if _LIBCPP_STD_VER > 11
 template <class _Iter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 reverse_iterator<_Iter> make_reverse_iterator(_Iter __i)
 {
     return reverse_iterator<_Iter>(__i);
 }
 #endif
 
 template <class _Container>
 class _LIBCPP_TYPE_VIS_ONLY back_insert_iterator
typedef typename conditional<
             is_reference<__reference>::value,
             typename remove_reference<__reference>::type&&,
             __reference
         >::type reference;
 #else
     typedef typename iterator_traits<iterator_type>::reference reference;
 #endif
 
-    _LIBCPP_INLINE_VISIBILITY move_iterator() : __i() {}
-    _LIBCPP_INLINE_VISIBILITY explicit move_iterator(_Iter __x) : __i(__x) {}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator() : __i() {}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 explicit move_iterator(_Iter __x) : __i(__x) {}
     template <class _Up> _LIBCPP_INLINE_VISIBILITY move_iterator(const move_iterator<_Up>& __u)
         : __i(__u.base()) {}
-    _LIBCPP_INLINE_VISIBILITY _Iter base() const {return __i;}
-    _LIBCPP_INLINE_VISIBILITY reference operator*() const {
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 _Iter base() const {return __i;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reference operator*() const {
       return static_cast<reference>(*__i);
     }
-    _LIBCPP_INLINE_VISIBILITY pointer  operator->() const { return __i;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator& operator++() {++__i; return *this;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator  operator++(int)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 pointer  operator->() const { return __i;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator& operator++() {++__i; return *this;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator  operator++(int)
         {move_iterator __tmp(*this); ++__i; return __tmp;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator& operator--() {--__i; return *this;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator  operator--(int)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator& operator--() {--__i; return *this;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator  operator--(int)
         {move_iterator __tmp(*this); --__i; return __tmp;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator  operator+ (difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator  operator+ (difference_type __n) const
         {return move_iterator(__i + __n);}
-    _LIBCPP_INLINE_VISIBILITY move_iterator& operator+=(difference_type __n)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator& operator+=(difference_type __n)
         {__i += __n; return *this;}
-    _LIBCPP_INLINE_VISIBILITY move_iterator  operator- (difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator  operator- (difference_type __n) const
         {return move_iterator(__i - __n);}
-    _LIBCPP_INLINE_VISIBILITY move_iterator& operator-=(difference_type __n)
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 move_iterator& operator-=(difference_type __n)
         {__i -= __n; return *this;}
-    _LIBCPP_INLINE_VISIBILITY reference         operator[](difference_type __n) const
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 reference         operator[](difference_type __n) const
     {
       return static_cast<reference>(__i[__n]);
     }
 };
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator==(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() == __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator<(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() < __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator!=(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() != __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator>(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() > __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator>=(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() >= __y.base();
 }
 
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 bool
 operator<=(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() <= __y.base();
 }
 
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 auto
 operator-(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 -> decltype(__x.base() - __y.base())
 {
     return __x.base() - __y.base();
 }
 #else
 template <class _Iter1, class _Iter2>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 typename move_iterator<_Iter1>::difference_type
 operator-(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
 {
     return __x.base() - __y.base();
 }
 #endif
 
 template <class _Iter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 move_iterator<_Iter>
 operator+(typename move_iterator<_Iter>::difference_type __n, const move_iterator<_Iter>& __x)
 {
     return move_iterator<_Iter>(__x.base() + __n);
 }
 
 template <class _Iter>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 
 move_iterator<_Iter>
 make_move_iterator(_Iter __i)
 {
     return move_iterator<_Iter>(__i);
 }
 
 // __wrap_iter
 

 end(_Tp (&__array)[_Np])
 {
     return __array + _Np;
 }
 
 #if !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_TRAILING_RETURN)
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto
 begin(_Cp& __c) -> decltype(__c.begin())
 {
     return __c.begin();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto
 begin(const _Cp& __c) -> decltype(__c.begin())
 {
     return __c.begin();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto
 end(_Cp& __c) -> decltype(__c.end())
 {
     return __c.end();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto
 end(const _Cp& __c) -> decltype(__c.end())
 {
     return __c.end();
 }
 
 #if _LIBCPP_STD_VER > 11
 
 template <class _Tp, size_t _Np>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 reverse_iterator<_Tp*> rbegin(_Tp (&__array)[_Np])
 {
     return reverse_iterator<_Tp*>(__array + _Np);
 }
 
 template <class _Tp, size_t _Np>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 reverse_iterator<_Tp*> rend(_Tp (&__array)[_Np])
 {
     return reverse_iterator<_Tp*>(__array);
 }
 
 template <class _Ep>
 inline _LIBCPP_INLINE_VISIBILITY
 reverse_iterator<const _Ep*> rbegin(initializer_list<_Ep> __il)

 template <class _Cp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 auto cend(const _Cp& __c) -> decltype(_VSTD::end(__c))
 {
     return _VSTD::end(__c);
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto rbegin(_Cp& __c) -> decltype(__c.rbegin())
 {
     return __c.rbegin();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto rbegin(const _Cp& __c) -> decltype(__c.rbegin())
 {
     return __c.rbegin();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto rend(_Cp& __c) -> decltype(__c.rend())
 {
     return __c.rend();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto rend(const _Cp& __c) -> decltype(__c.rend())
 {
     return __c.rend();
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto crbegin(const _Cp& __c) -> decltype(_VSTD::rbegin(__c))
 {
     return _VSTD::rbegin(__c);
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 auto crend(const _Cp& __c) -> decltype(_VSTD::rend(__c))
 {
     return _VSTD::rend(__c);
 }
 
 #endif
 
 

test/std/containers/sequences/array/at.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // XFAIL: libcpp-no-exceptions
 // <array>
 
-// reference operator[] (size_type)
+// reference operator[] (size_type); // constexpr in C++1z
 // const_reference operator[] (size_type); // constexpr in C++14
-// reference at (size_type)
+// reference at (size_type); // constexpr in C++1z
 // const_reference at (size_type); // constexpr in C++14
 
 #include <array>
 #include <cassert>
 
 #include "test_macros.h"
 
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
+#if TEST_STD_VER > 14
+constexpr auto constexpr_array_usage()
+{
+    typedef double T;
+    typedef std::array<T, 3> C;
+    C c = {1, 2, 3.5};
+
+    T &t1 = c.at(0);
+    t1 = 0;
+
+    T &t2 = c.at(2);
+    t2 = 2.5;
+    return c;
+}
+#endif
+
 int main()
 {
     {
         typedef double T;
         typedef std::array<T, 3> C;
         C c = {1, 2, 3.5};
         C::reference r1 = c.at(0);
         assert(r1 == 1);
#if TEST_STD_VER > 11
         constexpr T t1 = c.at(0);
         static_assert (t1 == 1, "");
 
         constexpr T t2 = c.at(2);
         static_assert (t2 == 3.5, "");
     }
 #endif
 
+#if TEST_STD_VER > 14
+    {
+        constexpr auto c = constexpr_array_usage();
+        static_assert (c.at(0) == 0);
+        static_assert (c.at(2) == 2.5);
+    }
+#endif
+
+
 }

test/std/containers/sequences/array/begin.pass.cpp

 
 #include <array>
 #include <cassert>
 
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
+
+#if TEST_STD_VER > 14
+constexpr auto constexpr_array_usage()
+{
+    typedef double T;
+    typedef std::array<T, 3> C;
+    C c = {1, 2, 3.5};
+    C::iterator i = c.begin();
+    *i = 5.5;
+    return c;
+}
+#endif
+
 int main()
 {
     {
         typedef double T;
         typedef std::array<T, 3> C;
         C c = {1, 2, 3.5};
         C::iterator i;
         i = c.begin();
         assert(*i == 1);
         assert(&*i == c.data());
         *i = 5.5;
         assert(c[0] == 5.5);
     }
+
+
+#if TEST_STD_VER > 14
+    {
+        constexpr c = constexpr_array_usage();
+        static_assert(c[0] == 5.5);
+    }
+#endif
 }

test/std/containers/sequences/array/front_back.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // <array>
 
-// reference front();
-// reference back();
+// reference front(); // constexpr in C++1z
+// reference back(); // constexpr in C++1z
 // const_reference front(); // constexpr in C++14
 // const_reference back(); // constexpr in C++14
 
 #include <array>
 #include <cassert>
 
 #include "test_macros.h"
 
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
+#if TEST_STD_VER > 14
+constexpr auto constexpr_array_usage()
+{
+    typedef double T;
+    typedef std::array<T, 3> C;
+    C c = {1, 2, 3.5};
+
+    T &t1 = c.front();
+    t1 = 0;
+    T &t2 = c.back();
+    t2 = 2.5;
+    return c;
+}
+#endif
+
+
 int main()
 {
     {
         typedef double T;
         typedef std::array<T, 3> C;
         C c = {1, 2, 3.5};
 
         C::reference r1 = c.front();
#if TEST_STD_VER > 11
         constexpr T t1 = c.front();
         static_assert (t1 == 1, "");
 
         constexpr T t2 = c.back();
         static_assert (t2 == 3.5, "");
     }
 #endif
 
+#if TEST_STD_VER > 14
+    {
+        constexpr auto c = constexpr_array_usage();
+        static_assert (c.front() == 0);
+        static_assert (c.back() == 2.5);
+    }
+#endif
+
+
 }

test/std/containers/sequences/array/indexing.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // <array>
 
-// reference operator[] (size_type)
+// reference operator[] (size_type); // constexpr in C++1z
 // const_reference operator[] (size_type); // constexpr in C++14
-// reference at (size_type)
+// reference at (size_type);  // constexpr in C++1z
 // const_reference at (size_type); // constexpr in C++14
 
 #include <array>
 #include <cassert>
 
 #include "test_macros.h"
 
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
+
+#if TEST_STD_VER > 14
+constexpr auto constexpr_array_usage()
+{
+    typedef double T;
+    typedef std::array<T, 3> C;
+    C c = {1, 2, 3.5};
+
+    T &t1 = c[0];
+    t1 = 0;
+
+    T &t2 = c[2];
+    t2 = 2.5;
+    return c;
+}
+#endif
+
+
 int main()
 {
     {
         typedef double T;
         typedef std::array<T, 3> C;
         C c = {1, 2, 3.5};
         C::reference r1 = c[0];
         assert(r1 == 1);
#if TEST_STD_VER > 11
         constexpr T t1 = c[0];
         static_assert (t1 == 1, "");
 
         constexpr T t2 = c[2];
         static_assert (t2 == 3.5, "");
     }
 #endif
 
+#if TEST_STD_VER > 14
+    {
+        constexpr auto c = constexpr_array_usage();
+        static_assert (c[0] == 0);
+        static_assert (c[2] == 2.5);
+    }
+#endif
+
 }

test/std/containers/sequences/array/iterators.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // <array>
 
 // iterator, const_iterator
 
 #include <array>
 #include <iterator>
 #include <cassert>
+#include "test_macros.h"
 
 int main()
 {
     {
     typedef std::array<int, 5> C;
     C c;
     C::iterator i;
     i = c.begin();
#if _LIBCPP_STD_VER > 11
 
         assert ( std::begin(c)   == std::end(c));
         assert ( std::rbegin(c)  == std::rend(c));
         assert ( std::cbegin(c)  == std::cend(c));
         assert ( std::crbegin(c) == std::crend(c));
         }
     }
 #endif
+
+
+#if TEST_STD_VER > 14
+    { // P0031 testing conextpr versions of iterators
+        {
+        typedef std::array<int, 5> C;
+
+        constexpr C c{};
+        static_assert ( c.begin()   == std::begin(c));
+        static_assert ( c.cbegin()  == std::cbegin(c));
+        static_assert ( c.rbegin()  == std::rbegin(c));
+        static_assert ( c.crbegin() == std::crbegin(c));
+        static_assert ( c.end()     == std::end(c));
+        static_assert ( c.cend()    == std::cend(c));
+        static_assert ( c.rend()    == std::rend(c));
+        static_assert ( c.crend()   == std::crend(c));
+
+        static_assert ( std::begin(c)   != std::end(c));
+        static_assert ( std::rbegin(c)  != std::rend(c));
+        static_assert ( std::cbegin(c)  != std::cend(c));
+        static_assert ( std::crbegin(c) != std::crend(c));
+        }
+        {
+        typedef std::array<int, 0> C;
+        constexpr C::iterator ii1{}, ii2{};
+        constexpr C::iterator ii4 = ii1;
+        constexpr C::const_iterator cii{};
+        static_assert ( ii1 == ii2 );
+        static_assert ( ii1 == ii4 );
+
+        static_assert (!(ii1 != ii2 ));
+
+        static_assert ( (ii1 == cii ));
+        static_assert ( (cii == ii1 ));
+        static_assert (!(ii1 != cii ));
+        static_assert (!(cii != ii1 ));
+        static_assert (!(ii1 <  cii ));
+        static_assert (!(cii <  ii1 ));
+        static_assert ( (ii1 <= cii ));
+        static_assert ( (cii <= ii1 ));
+        static_assert (!(ii1 >  cii ));
+        static_assert (!(cii >  ii1 ));
+        static_assert ( (ii1 >= cii ));
+        static_assert ( (cii >= ii1 ));
+        static_assert (cii - ii1 == 0);
+        static_assert (ii1 - cii == 0);
+
+        constexpr C c{};
+        static_assert ( c.begin()   == std::begin(c));
+        static_assert ( c.cbegin()  == std::cbegin(c));
+        static_assert ( c.rbegin()  == std::rbegin(c));
+        static_assert ( c.crbegin() == std::crbegin(c));
+        static_assert ( c.end()     == std::end(c));
+        static_assert ( c.cend()    == std::cend(c));
+        static_assert ( c.rend()    == std::rend(c));
+        static_assert ( c.crend()   == std::crend(c));
+
+        static_assert ( std::begin(c)   == std::end(c));
+        static_assert ( std::rbegin(c)  == std::rend(c));
+        static_assert ( std::cbegin(c)  == std::cend(c));
+        static_assert ( std::crbegin(c) == std::crend(c));
+        }
+    }
+#endif
 }

test/std/iterators/iterator.primitives/iterator.operations/advance.pass.cpp

 template <class It>
 void
 test(It i, typename std::iterator_traits<It>::difference_type n, It x)
 {
     std::advance(i, n);
     assert(i == x);
 }
 
+
+#if TEST_STD_VER > 14
+template <class It>
+constexpr
+auto
+static_test(It i, typename std::iterator_traits<It>::difference_type n)
+{
+    std::advance(i, n);
+    return i;
+}
+#endif
+
 int main()
 {
+    {
         const char* s = "1234567890";
         test(input_iterator<const char*>(s), 10, input_iterator<const char*>(s+10));
         test(forward_iterator<const char*>(s), 10, forward_iterator<const char*>(s+10));
         test(bidirectional_iterator<const char*>(s+5), 5, bidirectional_iterator<const char*>(s+10));
         test(bidirectional_iterator<const char*>(s+5), -5, bidirectional_iterator<const char*>(s));
         test(random_access_iterator<const char*>(s+5), 5, random_access_iterator<const char*>(s+10));
         test(random_access_iterator<const char*>(s+5), -5, random_access_iterator<const char*>(s));
         test(s+5, 5, s+10);
         test(s+5, -5, s);
     }
+
+#if TEST_STD_VER > 14
+    {
+        constexpr const char* s = "1234567890";
+        static_assert(static_test(s, 10) == s+10);
+        static_assert(static_test(s+5, 5) == s+10);
+        static_assert(static_test(s+5, -5) == s);
+    }
+#endif
+}
+

test/std/iterators/iterator.primitives/iterator.operations/distance.pass.cpp

 void
 test(It first, It last, typename std::iterator_traits<It>::difference_type x)
 {
     assert(std::distance(first, last) == x);
 }
 
 int main()
 {
+    {
         const char* s = "1234567890";
         test(input_iterator<const char*>(s), input_iterator<const char*>(s+10), 10);
         test(forward_iterator<const char*>(s), forward_iterator<const char*>(s+10), 10);
         test(bidirectional_iterator<const char*>(s), bidirectional_iterator<const char*>(s+10), 10);
         test(random_access_iterator<const char*>(s), random_access_iterator<const char*>(s+10), 10);
         test(s, s+10, 10);
     }
+
+
+#if TEST_STD_VER > 14
+    {
+        constexpr const char* s = "1234567890";
+        static_assert(std::distance(s, s+10) == 10);
+    }
+#endif
+
+}

test/std/iterators/iterator.primitives/iterator.operations/next.pass.cpp

 void
 test(It i, It x)
 {
     assert(std::next(i) == x);
 }
 
 int main()
 {
+    {
         const char* s = "1234567890";
         test(input_iterator<const char*>(s), 10, input_iterator<const char*>(s+10));
         test(forward_iterator<const char*>(s), 10, forward_iterator<const char*>(s+10));
         test(bidirectional_iterator<const char*>(s), 10, bidirectional_iterator<const char*>(s+10));
         test(random_access_iterator<const char*>(s), 10, random_access_iterator<const char*>(s+10));
         test(s, 10, s+10);
 
         test(input_iterator<const char*>(s), input_iterator<const char*>(s+1));
         test(forward_iterator<const char*>(s), forward_iterator<const char*>(s+1));
         test(bidirectional_iterator<const char*>(s), bidirectional_iterator<const char*>(s+1));
         test(random_access_iterator<const char*>(s), random_access_iterator<const char*>(s+1));
         test(s, s+1);
     }
+
+#if TEST_STD_VER > 14
+    {
+        constexpr const char* s = "1234567890";
+        static_assert(std::next(s, 10) == s+10);
+        static_assert(std::next(s) == s+1);
+    }
+#endif
+
+}

test/std/iterators/iterator.primitives/iterator.operations/prev.pass.cpp

 void
 test(It i, It x)
 {
     assert(std::prev(i) == x);
 }
 
 int main()
 {
+    {
         const char* s = "1234567890";
         test(bidirectional_iterator<const char*>(s+10), 10, bidirectional_iterator<const char*>(s));
         test(random_access_iterator<const char*>(s+10), 10, random_access_iterator<const char*>(s));
         test(s+10, 10, s);
 
         test(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s));
         test(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s));
         test(s+1, s);
     }
+
+#if TEST_STD_VER > 14
+    {
+        constexpr const char* s = "1234567890";
+        static_assert(std::prev(s+10, 10) == s);
+        static_assert(std::prev(s+1) == s);
+    }
+#endif
+
+}