libstdc++-v3/testsuite/20_util/optional/constexpr/observers/4.cc

   1 // { dg-options "-std=gnu++17" }
   2 // { dg-do compile { target c++17 }  }
   3
   4 // Copyright (C) 2013-2021 Free Software Foundation, Inc.
   5 //
   6 // This file is part of the GNU ISO C++ Library.  This library is free
   7 // software; you can redistribute it and/or modify it under the
   8 // terms of the GNU General Public License as published by the
   9 // Free Software Foundation; either version 3, or (at your option)
  10 // any later version.
  11
  12 // This library is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // You should have received a copy of the GNU General Public License along
  18 // with this library; see the file COPYING3.  If not see
  19 // <http://www.gnu.org/licenses/>.
  20
  21 #include <optional>
  22
  23 struct value_type
  24 {
  25   int i;
  26 };
  27
  28 void test01()
  29 {
  30   constexpr std::optional<value_type> o { value_type { 51 } };
  31   constexpr value_type fallback { 3 };
  32   static_assert( o.value_or(fallback).i == 51 );
  33   static_assert( o.value_or(fallback).i == (*o).i );
  34 }
  35
  36 void test02()
  37 {
  38   constexpr std::optional<value_type> o;
  39   constexpr value_type fallback { 3 };
  40   static_assert( o.value_or(fallback).i == 3 );
  41 }
  42
  43 template<typename T>
  44   constexpr std::optional<value_type>
  45   make_rvalue(T t)
  46   { return std::optional<value_type>{t}; }
  47
  48 void test03()
  49 {
  50   constexpr value_type fallback { 3 };
  51   static_assert( make_rvalue(value_type{51}).value_or(fallback).i == 51 );
  52 }
  53
  54 void test04()
  55 {
  56   constexpr value_type fallback { 3 };
  57   static_assert( make_rvalue(std::nullopt).value_or(fallback).i == 3 );
  58 }
  59
  60 int main()
  61 {
  62   test01();
  63   test02();
  64   test03();
  65   test04();
  66 }