To allow users to use BSON\PackedArray instances like array, the class should implement functionality similar to ArrayAccess. This would allow the following uses:

// Before
$packedArray->get(0);
// After
$packedArray[0];

// Before
$packedArray->has(0);
// After
isset($packedArray[0]);

Since instances of the class are a read-only, the following are expected to throw:

$packedArray[0] = 'foo';
$packedArray[] = 'foo';
unset($packedArray[0]);

Accessing invalid offsets should also throw (e.g. string offsets, negative values, out-of-bounds keys):

$packedArray['foo'];
$packedArray[-1];