libcxx/test/std/utilities/optional/optional.nullopt/nullopt_t.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 // <optional>
  11
  12 // struct nullopt_t{see below};
  13 // inline constexpr nullopt_t nullopt(unspecified);
  14
  15 // [optional.nullopt]/2:
  16 //   Type nullopt_t shall not have a default constructor or an initializer-list
  17 //   constructor, and shall not be an aggregate.
  18
  19 #include <optional>
  20 #include <type_traits>
  21
  22 #include "test_macros.h"
  23
  24 using std::nullopt_t;
  25 using std::nullopt;
  26
  27 constexpr bool test()
  28 {
  29     nullopt_t foo{nullopt};
  30     (void)foo;
  31     return true;
  32 }
  33
  34 int main(int, char**)
  35 {
  36     static_assert(std::is_empty_v<nullopt_t>);
  37     static_assert(!std::is_default_constructible_v<nullopt_t>);
  38
  39     static_assert(std::is_same_v<const nullopt_t, decltype(nullopt)>);
  40     static_assert(test());
  41
  42   return 0;
  43 }