class foo {
    var $bar = array();

    function baz($data) {
        $this->bar['data'] = $data; <---- works in php 5.6, not working in php 7.1
    }
}

function __construct(){
    $this->bar = array();
}

object(foo)#1 (1) {
  ["bar"]=>
  array(1) {
    ["data"]=>
    int(22)
  }
}

function __construct(){
    $this->bar = array();
}