libcxx/test/std/utilities/utility/as_const/as_const.pass.cpp

   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
  18 struct S {int i;};
  19 bool operator==(const S& x, const S& y) { return x.i == y.i; }
  20 bool operator==(const volatile S& x, const volatile S& y) { return x.i == y.i; }
  21
  22 template<typename 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
  38 int main(int, char**)
  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   return 0;
  48 }