Completing the simulator: returning the allowable actions

Now we are ready to complete the simulator object, by implementing the service of returning, for a given state, all the applicable actions. This is done by the get_applicable_action_sets method implementation. The final code for our example is:

void 
simulator::
get_applicable_action_sets( std::
                            list<plansim::action_set::const_ptr>& as ) 
    const
{
  // Creating an action set
  std::list<plansim::action::const_ptr> action_list;

  for( unsigned int from = 0; from < towers_.size(); from++ ) {
    
    // from tower must have at least one disk
    if( towers_[ from ].size() == 0 ) {
      continue;
    }

    for( unsigned int to = 0; to < towers_.size(); to++ ) {

      // Moves to the same tower are not allowed
      if( to == from ) {
        continue;
      }

      // Picks the disk in to tower, -1 if no disk is present
      int disk_in_to_tower;
      if( towers_[ to ].size() == 0 ) {
        disk_in_to_tower = -1;
      } else {
        disk_in_to_tower = towers_[ to ].back();
      }

      // Checks if disk may be moved
      if( towers_[ from ].back() > disk_in_to_tower ) {
        // Disk may be moved, action is created
        action_list.clear();
        plansim::action::const_ptr ap;
        ap.reset( new move_disk_action( towers_[ from ].back(), 
                                        from, to ) );
        action_list.push_back( ap );
        plansim::action_set::const_ptr 
          asp( new plansim::action_set( action_list ) );
        as.push_back( asp );	  
      }
    }
  }
}

Plansim supports the use of simultaneous actions, that is, actions that may be applied together at the same instant. In order to do so the method interface expects plansim::action_sets to be created. In our case every set contains a single element.