Fatal error: Method name must be a string - php

Question

I'm getting error:
Fatal error: Method name must be a string in C:\xampp\htdocs\index.php on line 15"
LINE 15:
$obj = new $url[0]();
CODE:
<?php
error_reporting(E_ALL ^ E_NOTICE);
$url = $_GET['url'];
$url = explode('/', $url);
if (!file_exists('controllers/' . $url[0] . '.php')) {
$url[0] = 'error'; // error kontroleris
}
require 'controllers/' . $url[0] . '.php';
$obj = new $url[0]();
$obj->$url[1]();
BTW.: Script is not finished yet.

Answer 1

Actually, this syntax:
$urls = array('DOMDocument');
$dom = new $urls[0]('');
var_dump( $dom );
... is valid even in PHP 5.2 (proof). But this line...
$obj->$url[1]();
... is pretty damn able (another proof) to throw exactly the same error as you've shown, as you don't check for url array length anywhere in your code.

Answer 2

$_GET['url'] = 'foo/bar'; // temp set $_GET
$url = $_GET['url'];
$url = explode('/', $url);
if (file_exists('controllers/' . $url[0] . '.php')){
require 'controllers/' . $url[0] . '.php';
}else{
$url[0] = 'error';
}
$obj = new URL;
if(method_exists($obj,$url[0])){ // test that method exists
echo $obj->$url[0](); // or whatever your handling may be
}
class URL{
public function error(){
$return = 'this is for the error handling';
return $return;
}
}