Sequence
A sequence is an ordered collection of values accessed by integer index starting from 0. PHP arrays natively act as sequences when keys are consecutive integers. The ds extension provides a dedicated Ds\Sequence interface implemented by Ds\Vector and Ds\Deque.
Unlike sets or maps, sequences allow duplicate values and maintain insertion order.
<?php
use Ds\Vector;
$seq = new Vector([1, 2, 3, 4]);
$seq->push(5);
echo $seq->get(2); // 3
echo $seq->count(); // 5
?>