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