策略模式

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<?php <?php interface math{     public function calc($op1,$op2); }   class mathadd implements math{     public function calc($op1,$op2){         return $op1+$op2;     } } class mathsub implements math{     public function calc($op1,$op2){         return $op1-$op2;     } } class mathmul implements math{     public function calc($op1,$op2){         return $op1*$op2;     } } class mathdiv implements math{     public function calc($op1,$op2){         return $op1/$op2;     } }   class cmath{     protected $calc = null;     public function __construct($type){         $calc = "math".$type;         $this->calc = new $calc();     }     public function calc($op1,$op2){         return $this->calc->calc($op1,$op2);     } }   $type = $_POST['op']; $cmath = new cmath($type); echo $cmath->calc($op1, $op2);