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

   1 // { dg-do compile { target c++17 }  }
   2
   3 // Copyright (C) 2013-2022 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License along
  17 // with this library; see the file COPYING3.  If not see
  18 // <http://www.gnu.org/licenses/>.
  19
  20 #include <optional>
  21
  22 struct value_type
  23 {
  24   int i;
  25 };
  26
  27 void test01()
  28 {
  29   constexpr std::optional<value_type> o { value_type { 51 } };
  30   constexpr value_type fallback { 3 };
  31   static_assert( o.value_or(fallback).i == 51 );
  32   static_assert( o.value_or(fallback).i == (*o).i );
  33 }
  34
  35 void test02()
  36 {
  37   constexpr std::optional<value_type> o;
  38   constexpr value_type fallback { 3 };
  39   static_assert( o.value_or(fallback).i == 3 );
  40 }
  41
  42 template<typename T>
  43   constexpr std::optional<value_type>
  44   make_rvalue(T t)
  45   { return std::optional<value_type>{t}; }
  46
  47 void test03()
  48 {
  49   constexpr value_type fallback { 3 };
  50   static_assert( make_rvalue(value_type{51}).value_or(fallback).i == 51 );
  51 }
  52
  53 void test04()
  54 {
  55   constexpr value_type fallback { 3 };
  56   static_assert( make_rvalue(std::nullopt).value_or(fallback).i == 3 );
  57 }
  58
  59 int main()
  60 {
  61   test01();
  62   test02();
  63   test03();
  64   test04();
  65 }