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/**
* 抽象基类
*/
abstract class Unit
{
  /**
  *获取名称
  */
  abstract public function getName();
 
}
 
/**
* Cpu类
*/
class Cpu extends Unit
{
  public function getName()
  {
    return 'i am cpu';
  }
}
 
/**
* 内存类
*/
class Memory extends Unit
{
  public function getName()
  {
    return 'i am memory';
  }
}
 
/**
* 键盘类
*/
class Keyboard extends Unit
{
  public function getName()
  {
    return 'i am keyboard';
  }
}
 
/**
* 计算机类
*/
class Computer
{
  protected $_items = [];
 
  public function add(Unit $unit)
  {
    $this->_items[] = $unit;
  }
 
  public function print()
  {
    // 循环打印各个组成部分
    foreach ($this->_items as $item) {
      $item->getName();
    }
  }
}

/**
* 抽象基类
*/
abstract class Unit
{
  /**
  * 获取名称
  */
  abstract public function getName();
 
  /**
  * 用来接受访问者对象，回调访问者的visit方法
  * 非常关键的方法
  */
  public function accept(Visitor $visitor)
  {
    $method = visit . get_class($this);
    if (method_exists($visitor, $method)) {
      $visitor->$method($this);
    }
  }
}
 
/**
* Cpu类
*/
class Cpu extends Unit
{
  public function getName()
  {
    return 'i am cpu';
  }
}
 
/**
* Memory类
*/
class Memory extends Unit
{
  public function getName()
  {
    return 'i am memory';
  }
}
 
/**
* Keyboard类
*/
class Keyboard extends Unit
{
  public function getName()
  {
    return 'i am keyboard';
  }
}
 
/**
* Keyboard类
*/
interface Visitor
{
  public function visitCpu(Cpu $cpu);
  public function visitMemory(Memory $memory);
  public function visitKeyboard(Keyboard $keyboard);
}
 
/**
* 
*/
class PrintVisitor implements Visitor
{
  public function visitCpu(Cpu $cpu)
  {
    echo "hello, " . $cpu->getName() . "\n";
  }
 
  public function visitMemory(Memory $memory)
  {
    echo "hello, " . $memory->getName() . "\n";
  }
 
  public function visitKeyboard(Keyboard $keyboard)
  {
    echo "hello, " . $keyboard->getName() . "\n";
  }
}
 
/**
* 
*/
class Computer
{
  protected $_items = [];
 
  public function add(Unit $unit)
  {
    $this->_items[] = $unit;
  }
   
  /**
  * 调用各个组件的accept方法
  */
  public function accept(Visitor $visitor)
  {
    foreach ($this->_items as $item) {
      $item->accept($visitor);
    }
  }
}
 
$computer = new Computer();
$computer->add(new Cpu());
$computer->add(new Memory());
$computer->add(new Keyboard());
 
$printVisitor = new PrintVisitor();
$computer->print($printVisitor);
 
// 以上的代码将打印出  
hello, i am cpu
hello, i am memory
hello, i am keyboard