1 //===----------------------------------------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 // UNSUPPORTED: c++98, c++03
11 
12 // <string>
13 
14 // void swap(basic_string& c)
15 //     noexcept(!allocator_type::propagate_on_container_swap::value ||
16 //              __is_nothrow_swappable<allocator_type>::value);
17 //
18 //  In C++17, the standard says that swap shall have:
19 //     noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
20 //              allocator_traits<Allocator>::is_always_equal::value);
21 
22 // This tests a conforming extension
23 
24 #include <string>
25 #include <utility>
26 #include <cassert>
27 
28 #include "test_macros.h"
29 #include "test_allocator.h"
30 
31 template <class T>
32 struct some_alloc
33 {
34     typedef T value_type;
35 
36     some_alloc() {}
37     some_alloc(const some_alloc&);
38     void deallocate(void*, unsigned) {}
39 
40     typedef std::true_type propagate_on_container_swap;
41 };
42 
43 template <class T>
44 struct some_alloc2
45 {
46     typedef T value_type;
47 
48     some_alloc2() {}
49     some_alloc2(const some_alloc2&);
50     void deallocate(void*, unsigned) {}
51 
52     typedef std::false_type propagate_on_container_swap;
53     typedef std::true_type is_always_equal;
54 };
55 
56 int main()
57 {
58     {
59         typedef std::string C;
60         static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
61     }
62 #if defined(_LIBCPP_VERSION)
63     {
64         typedef std::basic_string<char, std::char_traits<char>, test_allocator<char>> C;
65         static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
66     }
67 #endif // _LIBCPP_VERSION
68     {
69         typedef std::basic_string<char, std::char_traits<char>, some_alloc<char>> C;
70 #if TEST_STD_VER >= 14
71     //  In c++14, if POCS is set, swapping the allocator is required not to throw
72         static_assert( noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
73 #else
74         static_assert(!noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
75 #endif
76     }
77 #if TEST_STD_VER >= 14
78     {
79         typedef std::basic_string<char, std::char_traits<char>, some_alloc2<char>> C;
80     //  if the allocators are always equal, then the swap can be noexcept
81         static_assert( noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
82     }
83 #endif
84 }
85