Through which method is the value invoked if magic getter is combined with getter

Question

If I use it like this (outside of a class):

    $user_agent = $user->user_agent;        

Method get_user_agent() is called in constructor.

Here magic __get calls method get_user_agent and not returning value of member variable user_agent.

How to avoid that?

class user
{
    private $user_agent;


    public function __get($key)
    {
        $value = null;

        if(method_exists($this, "get_$key"))
        {
            $value = $this->{"get_$key"}();
        }
        else
        {
            $value = $this->$key;
        }

        return $value;
    }


    public function get_user_agent()
    {
        $this->user_agent = $_SERVER['HTTP_USER_AGENT'];
    }

Answer 1

You forgot to return the value after setting it:

public function get_user_agent()
{
    $this->user_agent = $_SERVER['HTTP_USER_AGENT'];
    return $this->user_agent;
}

But this is actually quite confusing, because you would not expect a method prefixed with 'get' to assign/define anything first before returning it. That's what __set() is for. In this case you probably even want to do it in the __construct() method:

class user
{
    private $user_agent;

    public function __construct() {
        $this->user_agent = $_SERVER['HTTP_USER_AGENT'];
    }

    public function __get($key) {

        if(method_exists($this, "get_$key"))  {
            return $this->{"get_$key"}();
        } else {
            return isset($this->{$key}) ? $this->{$key} : null;
        }

    }

    public function __set($var, $val) {
        //only allow to set existent attributes
        if( isset($this->{$var} ) ) {
            $this->{$var} = $val;
        }
    }

    public function get_user_agent() {
        return $this->user_agent;
    }
}

So the get-method is not the place to assign the attribute. In the example above, it is assign in the constructor. But you can change/assign it later if you want:

$user = new user(); //constructor-method is called, $user_agent is set now

But you can also set it yourself later on:

$user->user_agent = $_SERVER['HTTP_USER_AGENT'];  //the magic __set()-method is called

echo 'Your user agent is: ' . $user->user_agent;