PHP命令链模式

<?php//命令链模式class Person{    public function eat(){        echo __FUNCTION__;        return $this;    }    public function dirink(){        echo __FUNCTION__;        return $this;    }    public function sleep(){        echo __FUNCTION__;        return $this;    }}$p = new Person();$p->eat();$p->dirink();$p->sleep();$p->eat()->dirink()->sleep();