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, c++11, c++14
11
12 // template <class T> constexpr add_const<T>& as_const(T& t) noexcept; // C++17
13 // template <class T> add_const<T>& as_const(const T&&) = delete; // C++17
14
15 #include <utility>
16 #include <cassert>
17
18 struct S {int i;};
operator ==(const S & x,const S & y)19 bool operator==(const S& x, const S& y) { return x.i == y.i; }
operator ==(const volatile S & x,const volatile S & y)20 bool operator==(const volatile S& x, const volatile S& y) { return x.i == y.i; }
21
22 template<typename T>
test(T & t)23 void 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
main()38 int main()
39 {
40 int i = 3;
41 double d = 4.0;
42 S s{2};
43 test(i);
44 test(d);
45 test(s);
46 }
47