libcxx/test/std/containers/sequences/array/front_back.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 // <array>
  10
  11 // reference front();  // constexpr in C++17
  12 // reference back();   // constexpr in C++17
  13
  14 #include <array>
  15 #include <cassert>
  16
  17 #include "test_macros.h"
  18
  19 // std::array is explicitly allowed to be initialized with A a = { init-list };.
  20 // Disable the missing braces warning for this reason.
  21 #include "disable_missing_braces_warning.h"
  22
  23
  24 TEST_CONSTEXPR_CXX17 bool tests()
  25 {
  26     {
  27         typedef double T;
  28         typedef std::array<T, 3> C;
  29         C c = {1, 2, 3.5};
  30
  31         C::reference r1 = c.front();
  32         assert(r1 == 1);
  33         r1 = 5.5;
  34         assert(c[0] == 5.5);
  35
  36         C::reference r2 = c.back();
  37         assert(r2 == 3.5);
  38         r2 = 7.5;
  39         assert(c[2] == 7.5);
  40     }
  41     {
  42         typedef double T;
  43         typedef std::array<T, 0> C;
  44         C c = {};
  45         ASSERT_SAME_TYPE(decltype(c.back()), C::reference);
  46         LIBCPP_ASSERT_NOEXCEPT(c.back());
  47         ASSERT_SAME_TYPE(decltype(c.front()), C::reference);
  48         LIBCPP_ASSERT_NOEXCEPT(c.front());
  49         if (c.size() > (0)) { // always false
  50             TEST_IGNORE_NODISCARD c.front();
  51             TEST_IGNORE_NODISCARD c.back();
  52         }
  53     }
  54     {
  55         typedef double T;
  56         typedef std::array<const T, 0> C;
  57         C c = {};
  58         ASSERT_SAME_TYPE(decltype( c.back()), C::reference);
  59         LIBCPP_ASSERT_NOEXCEPT(    c.back());
  60         ASSERT_SAME_TYPE(decltype( c.front()), C::reference);
  61         LIBCPP_ASSERT_NOEXCEPT(    c.front());
  62         if (c.size() > (0)) {
  63             TEST_IGNORE_NODISCARD c.front();
  64             TEST_IGNORE_NODISCARD c.back();
  65         }
  66     }
  67
  68     return true;
  69 }
  70
  71 int main(int, char**)
  72 {
  73     tests();
  74 #if TEST_STD_VER >= 17
  75     static_assert(tests(), "");
  76 #endif
  77     return 0;
  78 }