<?php
class World {

...


public function move($from, $to) {
	...
	
	//$this->map = array_fill(0, $x, array_fill(0, $y, ''));
	$this->map[$to['x']][$to['y']] = $this->map[$from['x']][$from['y']];
	$this->map[$from['x']][$from['y']] = '';
}

...
}