What is a good strategy for safely reading values out of a PHP array?

Question

I'm trying to read values from $_SESSION which may or may not be set, while avoiding undefined index warnings. I'm used to Python dicts, which have a d.get('key','default') method, which returns a default parameter if not found. I've resorted to this:

function array_get($a, $key, $default=NULL)
{
  if (isset($a) and isset($a[$key]))
    return $a[$key];
  else
    return $default;
}

$foo = array_get($_SESSION, 'foo');
if (!$foo) {
  // Do some foo initialization
}

Is there a better way to implement this strategy?

Answer 1

$foo = (isset($_SESSION['foo'])) ? $_SESSION['foo'] : NULL;

Answer 2

I would use array_key_exists instead of isset for the second condition. Isset will return false if $a[$key] === null which is problematic if you've intentionally set $a[$key] = null. Of course, this isn't a huge deal unless you set a $default value to something other than NULL.

function array_get($a, $key, $default=NULL)
{
  if (isset($a) and array_key_exists($key, $a))
    return $a[$key];
  else
    return $default;
}