gistfile1.php

<?php

class User{
  public $user_email = "johan@mail.com";
}

$obj = new User();

function return_stuff($key){
   return $obj->$key;
}


echo return_stuff("user_email");



// Solution: store $key in temporary variable:


class User2{
	public $mail = "johan@mail.com";
	public $name = "johan";
}


function return_stuff($key){
	$obj = new User2();
	$ret = $key;
	return $obj->$ret;
}

echo return_stuff("name");



// Solution 2: even no need for temp variable, just place $key inside brackets

class User3{
	public $mail = "johan@mail.com";
	public $name = "johan";
}


function return_stuff($key){
	$obj = new User3();
	return $obj->{$key};
}

echo return_stuff("name");


?>