There are different ways to resolve that. For example, one-liner for display desired value may be:
function foo()
{
return array('bar'=>1, 'baz'=>2);
}
$value = array_shift(array_intersect_key(foo(), array('baz'=>null))); //you want $value
-but this looks weird and may be it have sense to create debug function, like:
function getValueByKey(array $array, $key)
{
return $array[$key];
}
$value = getValueByKey(foo(), 'baz');