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 // const_reference front(); // constexpr in C++14
  14 // const_reference back();  // constexpr in C++14
  15
  16 #include <array>
  17 #include <cassert>
  18
  19 #include "test_macros.h"
  20
  21 // std::array is explicitly allowed to be initialized with A a = { init-list };.
  22 // Disable the missing braces warning for this reason.
  23 #include "disable_missing_braces_warning.h"
  24
  25 #if TEST_STD_VER > 14
  26 constexpr bool check_front( double val )
  27 {
  28     std::array<double, 3> arr = {1, 2, 3.5};
  29     return arr.front() == val;
  30 }
  31
  32 constexpr bool check_back( double val )
  33 {
  34     std::array<double, 3> arr = {1, 2, 3.5};
  35     return arr.back() == val;
  36 }
  37 #endif
  38
  39 int main(int, char**)
  40 {
  41     {
  42         typedef double T;
  43         typedef std::array<T, 3> C;
  44         C c = {1, 2, 3.5};
  45
  46         C::reference r1 = c.front();
  47         assert(r1 == 1);
  48         r1 = 5.5;
  49         assert(c[0] == 5.5);
  50
  51         C::reference r2 = c.back();
  52         assert(r2 == 3.5);
  53         r2 = 7.5;
  54         assert(c[2] == 7.5);
  55     }
  56     {
  57         typedef double T;
  58         typedef std::array<T, 3> C;
  59         const C c = {1, 2, 3.5};
  60         C::const_reference r1 = c.front();
  61         assert(r1 == 1);
  62
  63         C::const_reference r2 = c.back();
  64         assert(r2 == 3.5);
  65     }
  66     {
  67       typedef double T;
  68       typedef std::array<T, 0> C;
  69       C c = {};
  70       C const& cc = c;
  71       ASSERT_SAME_TYPE(decltype( c.back()), typename C::reference);
  72       ASSERT_SAME_TYPE(decltype(cc.back()), typename C::const_reference);
  73       LIBCPP_ASSERT_NOEXCEPT(    c.back());
  74       LIBCPP_ASSERT_NOEXCEPT(   cc.back());
  75       ASSERT_SAME_TYPE(decltype( c.front()), typename C::reference);
  76       ASSERT_SAME_TYPE(decltype(cc.front()), typename C::const_reference);
  77       LIBCPP_ASSERT_NOEXCEPT(    c.front());
  78       LIBCPP_ASSERT_NOEXCEPT(   cc.front());
  79       if (c.size() > (0)) { // always false
  80         TEST_IGNORE_NODISCARD c.front();
  81         TEST_IGNORE_NODISCARD c.back();
  82         TEST_IGNORE_NODISCARD cc.front();
  83         TEST_IGNORE_NODISCARD cc.back();
  84       }
  85     }
  86     {
  87       typedef double T;
  88       typedef std::array<const T, 0> C;
  89       C c = {{}};
  90       C const& cc = c;
  91       ASSERT_SAME_TYPE(decltype( c.back()), typename C::reference);
  92       ASSERT_SAME_TYPE(decltype(cc.back()), typename C::const_reference);
  93       LIBCPP_ASSERT_NOEXCEPT(    c.back());
  94       LIBCPP_ASSERT_NOEXCEPT(   cc.back());
  95       ASSERT_SAME_TYPE(decltype( c.front()), typename C::reference);
  96       ASSERT_SAME_TYPE(decltype(cc.front()), typename C::const_reference);
  97       LIBCPP_ASSERT_NOEXCEPT(    c.front());
  98       LIBCPP_ASSERT_NOEXCEPT(   cc.front());
  99       if (c.size() > (0)) {
 100         TEST_IGNORE_NODISCARD c.front();
 101         TEST_IGNORE_NODISCARD c.back();
 102         TEST_IGNORE_NODISCARD cc.front();
 103         TEST_IGNORE_NODISCARD cc.back();
 104       }
 105     }
 106 #if TEST_STD_VER > 11
 107     {
 108         typedef double T;
 109         typedef std::array<T, 3> C;
 110         constexpr C c = {1, 2, 3.5};
 111
 112         constexpr T t1 = c.front();
 113         static_assert (t1 == 1, "");
 114
 115         constexpr T t2 = c.back();
 116         static_assert (t2 == 3.5, "");
 117     }
 118 #endif
 119
 120 #if TEST_STD_VER > 14
 121     {
 122         static_assert (check_front(1),   "");
 123         static_assert (check_back (3.5), "");
 124     }
 125 #endif
 126
 127   return 0;
 128 }