Index Checking

The functional difference between array_key_exists($key, $array) and isset($array[$key]) is that isset returns false when the key exists but contains null. Functionality aside, there is a demonstrable performance difference.

$dataSet = array();
$size = 0x1FFFF;

$i = $size;
while ($i--)
	$dataSet[$i] = $i+1;

$start = microtime(true);

$i = $size;
while ($i--)
	array_key_exists($i, $dataSet); //isset($dataSet[$i]);

echo "Time: ". (microtime(true) - $start);

Sure enough, after averaging a few benchmarks together the outcome was clear.

isset

0.0248870849609

array_key_exists

0.604112148285

When performance is important target isset() when applicable. It's even possible to use a fall through to increase performance, here's an example from my Options class: if (!isset($this->_options[$resolvedName]) && !array_key_exists($resolvedName, $this->_options))

In the following test case there was no performance difference between usage of append or directly addressing an index.

$dataSet = array();
$size = 0x1FFFF;
$i = $size;

$start = microtime(true);

while ($i--)
	$dataSet[] = $i+1; //$dataSet[$i] = $i+1;

echo "Time: ". (microtime(true) - $start);