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

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <iterator>

// reverse_iterator

// template <RandomAccessIterator Iter1, RandomAccessIterator Iter2>
//   requires HasMinus<Iter2, Iter1>
// auto operator-(const reverse_iterator<Iter1>& x, const reverse_iterator<Iter2>& y) // constexpr in C++17
//  -> decltype(y.base() - x.base());

#include <iterator>
#include <cstddef>
#include <cassert>
#include <type_traits>

#include "test_macros.h"
#include "test_iterators.h"

template <class, class, class = void> struct HasMinus : std::false_type {};
template <class R1, class R2> struct HasMinus<R1, R2, decltype((R1() - R2(), void()))> : std::true_type {};

template <class It1, class It2>
TEST_CONSTEXPR_CXX17 void test(It1 l, It2 r, std::ptrdiff_t x) {
    const std::reverse_iterator<It1> r1(l);
    const std::reverse_iterator<It2> r2(r);
    assert((r1 - r2) == x);
}

TEST_CONSTEXPR_CXX17 bool tests() {
    using PC = const char*;
    char s[3] = {0};

    // Test same base iterator type
    test(s, s, 0);
    test(s, s+1, 1);
    test(s+1, s, -1);

    // Test different (but subtractable) base iterator types
    test(PC(s), s, 0);
    test(PC(s), s+1, 1);
    test(PC(s+1), s, -1);

    // Test non-subtractable base iterator types
    static_assert( HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<int*> >::value, "");
    static_assert( HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<const int*> >::value, "");
#if TEST_STD_VER >= 11
    static_assert(!HasMinus<std::reverse_iterator<int*>, std::reverse_iterator<char*> >::value, "");
    static_assert(!HasMinus<std::reverse_iterator<bidirectional_iterator<int*> >, std::reverse_iterator<bidirectional_iterator<int*> > >::value, "");
#endif

    return true;
}

int main(int, char**) {
    tests();
#if TEST_STD_VER > 14
    static_assert(tests(), "");
#endif
    return 0;
}