PHP: reflection, "non well formed numeric value encountered" setting array index -

i haven't been able find specific issue. in class need take associative array , put it's values in class variables. sub-arrays need converted objects. conversion objects happening in following code:

foreach ($value $key2 => $value2) {   $object = new $object_str($value2);   $this->$key[$object->getid()] = $object; } 

$value comes outer foreach loop.
$object_str contains name of object has created,
this: martkuper\onepagecrm\contacts\contactsurl

the input array this:

[   'url' => [     'type' => 'website',     'value' => 'google.com'   ] ] 

it should create contactsurl object , add $url class variable (which array) based on class' internal random id (uniqid()). because don't know how many 'url' entries input array have, needs happen dynamically. hence

$this->$key[$object->getid()] 

the error occurs on index of $key (url) array. seems doesn't take string index. i've tried putting hardcoded strings in

$this->$key['test]   

that doesn't work either. when put integer in

$this->$key[1] 

it work. converting string integer not option. break parser class used many other classes.

i've solved issue doing following:

$this->{$key}[$object->getid()] = $object; 

what happening tried take index of $key variable ($key[$object->getid()]) since $key isn't array, failed. needed take index of class variable $key represents instead.