Switching Classes during __construct() - php

Question

Let's take the following classes for a moment:
class member {
public $id;
public function __construct($id) {
$this->id = $id;
// Check user level
if ($this->check_user_level() == moderator) {
$this = new moderator($this->id);
}
}
private function check_user_level() {
// Return user level from system based on user ID
}
}
class moderator extends member {
public function show_moderator_tools() {
// etc.
}
}
==================
$user = new member($user_id);
The desired behavior is to have $user detect whether the user is authorized to have moderator access, and if so recast the user using the moderator class instead of member.
PHP forbids simply reassigning $this, so what appears to be the best solution would be one of the following:
Run check_user_level($id) as a regular function and using an if statement
$user_level = check_user_level($id);
if ($user_level == "moderator") {
$user = new moderator($id);
} else {
$user = new member($id);
}
Set a flag in the base class that can be used for a check/redefinition after initializing $user
$user = new member($id);
if ($user->flag = TRUE) {
$user = new moderator($id);
}
The latter feels like it's introducing a security flaw, especially since the flag (which could just as easily be $user->user_level, or similar, I guess) would have to be public to be able to check it afterward.
What I would like to do would be to just make one call to new member($id) and have it handle things automatically from there, without the need for if statements after the fact. Is there a way to do this?

Answer 1

You can of do this by introducing another class (lets call it user) and using the __call magic method in php and call_user_func_array for calling the methods.
The logic is something like this -
Create a user class that has no method except check_user_level. It checks proper details and assigns it's $obj to the instance of either member or moderator class.
Here is how the classes would look like (I've changed the functions to print something out)-
class user{
public function __construct($id) {
$this->id = $id;
if ($this->check_user_level() == "moderator") {
$this->obj = new moderator($this->id);
}else{
$this->obj = new member($this->id);
}
}
public function __call($method, $args){
call_user_func_array(array($this->obj,$method), $args);
}
public function __get($prop){
if(isset($this->obj->$prop)){
return $this->obj->$prop;
}
return NULL;
}
private function check_user_level() {
// Return user level from system based on user ID
if($this->id == 1){
return "moderator";
}
return "member";
}
}
class member {
public $id;
public function __construct($id) {
$this->id = $id;
}
public function show_message($arg){
var_dump($this->id.$arg);
}
}
class moderator extends member{
public function show_moderator_tools() {
var_dump($this->id ."My toolset!");
}
}
So, now you can simply call the user class and that will automatically decide if it's a member or a moderator and call the method if it exists.
//Trying out a few examples
//Creating a member user
$mem_obj = new user(213);
$mem_obj->show_message("New message");
//Creating a moderator user
$mod_obj = new user(1);
$mod_obj->show_moderator_tools();
/*
OUTPUTS
-------
string(14) "213New message"
string(12) "1My toolset!"
*/
But you need to be careful with these kind of hacks.
For instance -
//This will fail
//because mem_obj doesn't have show_moderator_tools()
$mem_obj->show_moderator_tools();
EDIT
You can similarly go ahead with redirecting to properties using __get.
I have modified the code above to add this method beneath __call.
//Testing it
var_dump($mem_obj->id);
//This is an illegal property
var_dump($mem_obj->illegelProperty);
/*
OUTPUTS
int(213)
NULL
*/