//实现一个简单的计算器
interface MathOp{
  public function calculation($num1,$num2);
}
//加法
class MathAdd implements MathOp{
  public function calculation($num1,$num2){
    return $num1 + $num2;
  }
}
//减法
class MathSub implements MathOp{
  public function calculation($num1,$num2){
    return $num1 - $num2;
  }
}
//乘法
class MathMulti implements MathOp{
  public function calculation($num1,$num2){
    return $num1 * $num2;
  }
}
//除法
class MathDiv implements MathOp{
  public function calculation($num1,$num2){
    return $num1 / $num2;
  }
}
class Op{
  protected $op_class = null;
  public function __construct($op_type){
    $this->op_class = 'Math' . $op_type;
  }
  public function get_result($num1,$num2){
    $cls = new $this->op_class;
    return $cls->calculation($num1,$num2);
  }
}
$obj = new Op('Add');
echo $obj->get_result(6,2);//8
$obj = new Op('Sub');
echo $obj->get_result(6,5);//1
$obj = new Op('Multi');
echo $obj->get_result(6,2);//12
$obj = new Op('Div');
echo $obj->get_result(6,2);//3