text: // { dg-options "-std=gnu++17" }
  // { dg-do run }
  
  // Copyright (C) 2013-2017 Free Software Foundation, Inc.
  //
  // This file is part of the GNU ISO C++ Library.  This library is free
  // software; you can redistribute it and/or modify it under the
  // terms of the GNU General Public License as published by the
  // Free Software Foundation; either version 3, or (at your option)
  // any later version.
  
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  // GNU General Public License for more details.
  
  // You should have received a copy of the GNU General Public License along
  // with this library; see the file COPYING3.  If not see
  // <http://www.gnu.org/licenses/>.
  
  #include <optional>
  #include <vector>
  #include <testsuite_hooks.h>
  
  int counter = 0;
  
  struct mixin_counter
  {
    mixin_counter() { ++counter; }
    mixin_counter(mixin_counter const&) { ++counter; }
    ~mixin_counter() { --counter; }
  };
  
  struct value_type : private mixin_counter { };
  
  int main()
  {
    using O = std::optional<value_type>;
  
    // Check std::nullopt_t and 'default' (= {}) assignment
  
    {
      O o;
      o = std::nullopt;
      VERIFY( !o );
    }
  
    {
      O o { std::in_place };
      o = std::nullopt;
      VERIFY( !o );
    }
  
    {
      O o;
      o = {};
      VERIFY( !o );
    }
  
    {
      O o { std::in_place };
      o = {};
      VERIFY( !o );
    }
    {
      std::optional<std::vector<int>> ovi{{1, 2, 3}};
      VERIFY(ovi->size() == 3);
      VERIFY((*ovi)[0] == 1 && (*ovi)[1] == 2 && (*ovi)[2] == 3);
      ovi = {4, 5, 6, 7};
      VERIFY(ovi->size() == 4);
      VERIFY((*ovi)[0] == 4 && (*ovi)[1] == 5 &&
  	   (*ovi)[2] == 6 && (*ovi)[3] == 7);
    }
    VERIFY( counter == 0 );
  }
  