1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 // UNSUPPORTED: c++03, c++11, c++14, c++17
10 // UNSUPPORTED: libcpp-no-concepts
11 
12 // constexpr decltype(auto) operator[](iter_difference_t<I> n) const
13 //   requires random_access_iterator<I>;
14 
15 #include <iterator>
16 
17 #include "test_macros.h"
18 #include "test_iterators.h"
19 
20 template<class Iter>
21 concept SubscriptEnabled = requires(Iter& iter) {
22   iter[1];
23 };
24 
25 constexpr bool test() {
26   int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
27 
28   {
29     std::counted_iterator iter(random_access_iterator<int*>{buffer}, 8);
30     for (int i = 1; i < 9; ++i)
31       assert(iter[i - 1] == i);
32   }
33   {
34     std::counted_iterator iter(contiguous_iterator<int*>{buffer}, 8);
35     for (int i = 1; i < 9; ++i)
36       assert(iter[i - 1] == i);
37   }
38 
39   {
40     const std::counted_iterator iter(random_access_iterator<int*>{buffer}, 8);
41     assert(iter[0] == 1);
42   }
43   {
44     const std::counted_iterator iter(contiguous_iterator<int*>{buffer}, 8);
45     assert(iter[7] == 8);
46   }
47 
48   {
49       static_assert( SubscriptEnabled<std::counted_iterator<random_access_iterator<int*>>>);
50       static_assert(!SubscriptEnabled<std::counted_iterator<bidirectional_iterator<int*>>>);
51   }
52 
53   return true;
54 }
55 
56 int main(int, char**) {
57   test();
58   static_assert(test());
59 
60   return 0;
61 }
62