within (function PopulateObjectArray)in class.GenericObjectCollection.php

$refObjArrayIndexObj = &$this->obj_array[$this_index];
i don't know what is the value of $refObjArrayIndexObj, because in this line
is the first time where $this->obj_array is used,
and i don't get the line where is asigned something to
$this->obj_array = (like this)
so i can't understand what is holding $refObjArrayIndexObj

following the code there is another line in (function RetrievePopulatedObjects)
$return_array[$counter] = $this->obj_array[$i];
and then
return($return_array);
but if $this->obj_array was never assigned with something,
the value of $return_array will be?.

Thank you, and congratulations.

complementing my question, i ask for this two lines because when i run the code
$uh= new UserHome();
$arUsers= $uh->GetallUsersWithFirstNameBeginningWith('l');
for ($i=0;i<=sizeof($arUsers)-1;$i++){
    print " " .$arUsers[$i]->GetField("last_name") . " " .
          $arUsers[$i]->GetField("first_name") . " " .
          $arUsers[$i]->GetField("username"). "<br/>\n";
};

i get the following error after i get the desired return.
john Doe
Jane Doe
Fatal error: Call to a member function GetField() on a non-object in C:\Apache2\Pruebas\ProPHP5\ch07\testuserhome.php on line 7
the error is referring to
$arUsers which is receiving the value from $return_array which implies obj_array