什么是代理模式？（实例说明）

<?php
//代理对象,一台打印机
class Printer { 
    public function printSth() {
        echo &#39;我可以打印<br>&#39;;
    }
}
//这是一个文印处理店,只文印,卖纸,不照相
class TextShop {
    private $printer;
    public function __construct(Printer $printer) {
        $this->printer = $printer;
    }
    //卖纸
    public function sellPaper() {
        echo &#39;give you some paper <br>&#39;;
    }
    //将代理对象有的功能交给代理对象处理
    public function __call($method, $args) {
        if(method_exists($this->printer, $method)) {
            $this->printer->$method($args);
        }
    }
}
//这是一个照相店,只文印,拍照,不卖纸
class PhotoShop {    
    private $printer;
    
    public function __construct(Printer $printer) {
        $this->printer = $printer;
    }
    
    public function takePhotos() {    //照相
        echo &#39;take photos for you <br>&#39;;
    }
    
    public function __call($method, $args) {    //将代理对象有的功能交给代理对象处理
        if(method_exists($this->printer, $method)) {
            $this->printer->$method($args);
        }
    }
}
$printer = new Printer();
$textShop = new TextShop($printer);
$photoShop = new PhotoShop($printer);
$textShop->printSth();
$photoShop->printSth();