best way append named array to array in PHP 5.2

I got used to this notation for creating empty arrays and add named elements to them when needed;

$array = [];

// in case there is an error
$array["error"][] = "new error message as element 0 of $array['error']";

Now I learned that the [] notation for arrays does not work in older versions of PHP, like PHP 5.2.

Instead I have to do;

$array = array(
  "error" => array()
);

array_push($array["error"], "new error message as element 0 of $array['error']");

This way is a little bit inconvenient in my case because the great thing about the first code snippet is that the "error" entry in $array is only created when there is an actual error, whereas in the latter case the entry (although empty) exists either way.

Is there a way to get similar 'functionality' (i.e. specifying/adding named elements when needed, not at initialisation) in a way that is also easily readable in PHP 5.2?

Solution

EDIT: The first code snippet in the original post was reading $array = array[];. The author corrected it after I posted this answer.

The first code snipped is incorrect. There is no such thing as array[]. The correct syntax is array().

$array = array();

// in case there is an error
$array["error"][] = "new error message as element 0 of $array['error']";

You don't have to worry about PHP versions. This syntax always worked on PHP since its dawn and it will probably work forever. Keep using it.