Access array returned by a function in php

I'm using a template engine that inserts code in my site where I want it.

I wrote a function to test for something which is quite easy:

myfunction() { return '($this->data["a"]["b"] ? true : false)'; }

The problem is, $this->data is private, and I can't access it everywhere, so I have to use getData(); which causes my problem.

$this->getData()['a']['b']

does not work, and assigning the value first doesn't either because it will be used directly in an if() block.

Any ideas?