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

source code of libcxx/test/std/utilities/utility/as_const/as_const.pass.cpp