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 // UNSUPPORTED: c++98, c++03, c++11, c++14
10 
11 // template <class T> constexpr add_const<T>& as_const(T& t) noexcept;      // C++17
12 // template <class T>           add_const<T>& as_const(const T&&) = delete; // C++17
13 
14 #include <utility>
15 #include <cassert>
16 
17 #include "test_macros.h"
18 
19 struct S {int i;};
20 bool operator==(const S& x, const S& y) { return x.i == y.i; }
21 bool operator==(const volatile S& x, const volatile S& y) { return x.i == y.i; }
22 
23 template<typename T>
24 void test(T& t)
25 {
26     static_assert(std::is_const<typename std::remove_reference<decltype(std::as_const                  (t))>::type>::value, "");
27     static_assert(std::is_const<typename std::remove_reference<decltype(std::as_const<               T>(t))>::type>::value, "");
28     static_assert(std::is_const<typename std::remove_reference<decltype(std::as_const<const          T>(t))>::type>::value, "");
29     static_assert(std::is_const<typename std::remove_reference<decltype(std::as_const<volatile       T>(t))>::type>::value, "");
30     static_assert(std::is_const<typename std::remove_reference<decltype(std::as_const<const volatile T>(t))>::type>::value, "");
31 
32     assert(std::as_const(t) == t);
33     assert(std::as_const<               T>(t) == t);
34     assert(std::as_const<const          T>(t) == t);
35     assert(std::as_const<volatile       T>(t) == t);
36     assert(std::as_const<const volatile T>(t) == t);
37 }
38 
39 int main(int, char**)
40 {
41     int i = 3;
42     double d = 4.0;
43     S s{2};
44     test(i);
45     test(d);
46     test(s);
47 
48   return 0;
49 }
50