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 
11 // constexpr decltype(auto) operator[](iter_difference_t<I> n) const
12 //   requires random_access_iterator<I>;
13 
14 #include <iterator>
15 
16 #include "test_macros.h"
17 #include "test_iterators.h"
18 
19 template<class Iter>
20 concept SubscriptEnabled = requires(Iter& iter) {
21   iter[1];
22 };
23 
24 constexpr bool test() {
25   int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
26 
27   {
28     std::counted_iterator iter(random_access_iterator<int*>{buffer}, 8);
29     for (int i = 1; i < 9; ++i)
30       assert(iter[i - 1] == i);
31   }
32   {
33     std::counted_iterator iter(contiguous_iterator<int*>{buffer}, 8);
34     for (int i = 1; i < 9; ++i)
35       assert(iter[i - 1] == i);
36   }
37 
38   {
39     const std::counted_iterator iter(random_access_iterator<int*>{buffer}, 8);
40     assert(iter[0] == 1);
41   }
42   {
43     const std::counted_iterator iter(contiguous_iterator<int*>{buffer}, 8);
44     assert(iter[7] == 8);
45   }
46 
47   {
48       static_assert( SubscriptEnabled<std::counted_iterator<random_access_iterator<int*>>>);
49       static_assert(!SubscriptEnabled<std::counted_iterator<bidirectional_iterator<int*>>>);
50   }
51 
52   return true;
53 }
54 
55 int main(int, char**) {
56   test();
57   static_assert(test());
58 
59   return 0;
60 }
61