使用Magic Methods了解Simple类

Question

I just started following a video series on OOP in PHP and have made the following class following one lecture. At first there was no __get and __set, because he showed us to how to deal with public variables. But for demonstrations sake the lecturer changed public $postal_code into protected $_postal_code. Basically what he showed was that he could change the original postal code that we set using

$adress->postal_code = "M422 3555";

into "ADDED PROTECTED VALUE" via this method

 protected function _postal_code_guess(){
        return 'ADDED PROTECTED VALUE';

Now the two main things I'm having trouble understanding is how do our __get and __set methods know what $name is? If I echo $name before anything in either the get or set methods it tells me it represents postal_code. But why is that? Where is it getting set that value?

The other thing I am a bit confused about is how the line $output.=",".$this->postal_code; is still working. Because we changed our original public $postal_code into protected $_postal_code;Doe-sent that mean we should change

$output.=",".$this->postal_code;

into

$output.=",".$this->_postal_code;

TLDR

1.How does our code know what $name is ?

1. Why are we still allowed to do $output.=",".$this->postal_code;, even when our variable was changed to protected _postal_code

Below is all the code

class Adress{

    public $country;
    public $province;
    public $city;
    public $adress;
    protected $_postal_code;

    // primary key of an adress
    protected $_adress_id;
    protected $_time_created;
    protected $_time_updated;

    function __get($name){

        if(!$this->_postal_code){
            $this->_postal_code = $this->_postal_code_guess();
        }

        // attempt to return a protected property by name
        $protected_property_name = "_".$name;
        if(property_exists($this,$protected_property_name)){
            return $this->$protected_property_name;
        }

        trigger_error("Undefined property via __get".$name);
        return null;    
    }

    function __set($name,$value){
        if('postal_code' == $name){
            $this->$name = $value;
            return;
        }

        trigger_error('Undefined or unallowed propert via __set()');

    }

    protected function _postal_code_guess(){
        return 'ADDED PROTECTED VALUE';
    }
    function display(){
        $output = '';

        $output.=$this->country;
        $output.="<br/>";
        $output.=$this->province;
        $output.=' '.$this->city;


  $output.=" ".$this->adress;
    $output.=",".$this->postal_code;
    return $output;
}

}

Here is the demo.php file where we run it

<?php
require 'index.php';
$adress = new Adress;
$adress->country = "Canada";
$adress->province = "Ontario";
$adress->city = "Toronto";
$adress->adress ="4324323 Bob Street";
$adress->postal_code = "M422 3555";
echo '<tt><pre>'.var_export($adress,TRUE).'</tt></pre>';
echo $adress->display();
echo '<h2>Test Protected Variables</h2>';
unset($adress->postal_code);
echo $adress->display();

Answer 1

There is a decent description of __get() and __set() magic methods in the official PHP Manual.

$this->postal_code works only thanks to __get() method, which - in your example - dynamically tries to find a property with underscore removed. It's not any of default PHP behaviors, just specific to your code.