libcxx/test/std/containers/views/span.elem/front.pass.cpp

   1 // -*- C++ -*-
   2 //===------------------------------ span ---------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===---------------------------------------------------------------------===//
   9 // UNSUPPORTED: c++03, c++11, c++14, c++17
  10
  11 // <span>
  12
  13 // constexpr reference front() const noexcept;
  14 //   Expects: empty() is false.
  15 //   Effects: Equivalent to: return *data();
  16 //
  17
  18
  19 #include <span>
  20 #include <cassert>
  21 #include <string>
  22
  23 #include "test_macros.h"
  24
  25
  26 template <typename Span>
  27 constexpr bool testConstexprSpan(Span sp)
  28 {
  29     LIBCPP_ASSERT(noexcept(sp.front()));
  30     return std::addressof(sp.front()) == sp.data();
  31 }
  32
  33
  34 template <typename Span>
  35 void testRuntimeSpan(Span sp)
  36 {
  37     LIBCPP_ASSERT(noexcept(sp.front()));
  38     assert(std::addressof(sp.front()) == sp.data());
  39 }
  40
  41 template <typename Span>
  42 void testEmptySpan(Span sp)
  43 {
  44     if (!sp.empty())
  45         [[maybe_unused]] auto res = sp.front();
  46 }
  47
  48 struct A{};
  49 constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
  50           int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
  51
  52 int main(int, char**)
  53 {
  54     static_assert(testConstexprSpan(std::span<const int>(iArr1, 1)), "");
  55     static_assert(testConstexprSpan(std::span<const int>(iArr1, 2)), "");
  56     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3)), "");
  57     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4)), "");
  58
  59     static_assert(testConstexprSpan(std::span<const int, 1>(iArr1, 1)), "");
  60     static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2)), "");
  61     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3)), "");
  62     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4)), "");
  63
  64
  65     testRuntimeSpan(std::span<int>(iArr2, 1));
  66     testRuntimeSpan(std::span<int>(iArr2, 2));
  67     testRuntimeSpan(std::span<int>(iArr2, 3));
  68     testRuntimeSpan(std::span<int>(iArr2, 4));
  69
  70
  71     testRuntimeSpan(std::span<int, 1>(iArr2, 1));
  72     testRuntimeSpan(std::span<int, 2>(iArr2, 2));
  73     testRuntimeSpan(std::span<int, 3>(iArr2, 3));
  74     testRuntimeSpan(std::span<int, 4>(iArr2, 4));
  75
  76     std::string s;
  77     testRuntimeSpan(std::span<std::string>   (&s, 1));
  78     testRuntimeSpan(std::span<std::string, 1>(&s, 1));
  79
  80     std::span<int, 0> sp;
  81     testEmptySpan(sp);
  82
  83     return 0;
  84 }