appending an array non-static progenitor category php

how i extend parent's options array child classes php?

i have something this:

class parentclass {

     open $options = array(
          'option1'=>'setting1'
     );

     //the rest functions follow
}

i insert options array child category but erasing any progenitor options. i've attempted doing something this, nonetheless haven't definitely got work yet:

class childclass extends parentclass {

     open $options = parent::options + array(
          'option2'=>'setting2'
     );

     //the rest functions follow
}

what best proceed something this?