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// <iterator>
10
11// reverse_iterator
12
13// template <RandomAccessIterator Iter1, RandomAccessIterator Iter2>
14// requires HasMinus<Iter2, Iter1>
15// auto operator-(const reverse_iterator<Iter1>& x, const reverse_iterator<Iter2>& y) // constexpr in C++17
16// -> decltype(y.base() - x.base());
17
18#include <iterator>
19#include <cstddef>
20#include <cassert>
21#include <type_traits>
22
23#include "test_macros.h"
24#include "test_iterators.h"
25
26template <class, class, class = void> struct HasMinus : std::false_type {};
27template <class R1, class R2> struct HasMinus<R1, R2, decltype((R1() - R2(), void()))> : std::true_type {};
28
29template <class It1, class It2>
30TEST_CONSTEXPR_CXX17 void test(It1 l, It2 r, std::ptrdiff_t x) {
31 const std::reverse_iterator<It1> r1(l);
32 const std::reverse_iterator<It2> r2(r);
33 assert((r1 - r2) == x);
34}
35
36TEST_CONSTEXPR_CXX17 bool tests() {
37 using PC = const char*;
38 char s[3] = {0};
39
40 // Test same base iterator type
41 test(s, s, 0);
42 test(s, s+1, 1);
43 test(s+1, s, -1);
44
45 // Test different (but subtractable) base iterator types
46 test(PC(s), s, 0);
47 test(PC(s), s+1, 1);
48 test(PC(s+1), s, -1);
49
50 // Test non-subtractable base iterator types
51 static_assert( HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<int*> >::value, "");
52 static_assert( HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<const int*> >::value, "");
53#if TEST_STD_VER >= 11
54 static_assert(!HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<char*> >::value, "");
55 static_assert(!HasMinus<std::reverse_iterator<bidirectional_iterator<int*> >, std::reverse_iterator<bidirectional_iterator<int*> > >::value, "");
56#endif
57
58 return true;
59}
60
61int main(int, char**) {
62 tests();
63#if TEST_STD_VER > 14
64 static_assert(tests(), "");
65#endif
66 return 0;
67}
68

source code of libcxx/test/std/iterators/predef.iterators/reverse.iterators/reverse.iter.nonmember/minus.pass.cpp