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

   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
  26 template <class, class, class = void> struct HasMinus : std::false_type {};
  27 template <class R1, class R2> struct HasMinus<R1, R2, decltype((R1() - R2(), void()))> : std::true_type {};
  28
  29 template <class It1, class It2>
  30 TEST_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
  36 TEST_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
  61 int main(int, char**) {
  62     tests();
  63 #if TEST_STD_VER > 14
  64     static_assert(tests(), "");
  65 #endif
  66     return 0;
  67 }