PHP SplPriorityQueue::rewind() Method: Usage and Examples

Implements Iterator::rewind as a no-op on the priority queue.

The examples focus on the operation itself, including the important distinction: next removes the current greatest-priority item.

What It Does

Use the examples below to observe the behavior on a small dataset before extending it to application code.

Syntax and Return Value

SplPriorityQueue::rewind()

The displayed signature describes the API or identifies any correction or optional dependency. When a parameter is optional, supply it only when the task requires it.

Example 1: Basic Use

Extracting consumes the top job; rewind cannot restore an already extracted priority-queue entry.

<?php
$priority = new SplPriorityQueue();
$priority->insert('job-4', 4);
$priority->insert('job-12', 12);
$priority->insert('job-7', 7);
$removed = $priority->extract();
$priority->rewind();
echo json_encode(["removed" => $removed, "current" => $priority->current()]);

Output from a successful local PHP 8.4 run:

{"removed":"job-12","current":"job-7"}

Example 2: Checking Behavior

Extracting consumes the top job; rewind cannot restore an already extracted priority-queue entry.

<?php
$priority = new SplPriorityQueue();
$priority->insert('job-2', 2);
$priority->insert('job-9', 9);
$priority->insert('job-5', 5);
$priority->insert('job-1', 1);
$removed = $priority->extract();
$priority->rewind();
echo json_encode(["removed" => $removed, "current" => $priority->current()]);

Output from a successful local PHP 8.4 run:

{"removed":"job-9","current":"job-5"}

Example 3: Practical Example

Extracting consumes the top job; rewind cannot restore an already extracted priority-queue entry.

<?php
$priority = new SplPriorityQueue();
$priority->insert('job-19', 19);
$priority->insert('job-3', 3);
$priority->insert('job-11', 11);
$removed = $priority->extract();
$priority->rewind();
echo json_encode(["removed" => $removed, "current" => $priority->current()]);

Output from a successful local PHP 8.4 run:

{"removed":"job-19","current":"job-11"}

Important Behavior and Edge Cases

Previously extracted entries are not restored, and iteration continues to consume the remaining queue.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Implements Iterator::rewind as a no-op on the priority queue.
• Previously extracted entries are not restored, and iteration continues to consume the remaining queue.
• next removes the current greatest-priority item.

Use SplPriorityQueue::rewind when its documented behavior matches the problem. Test the relevant edge cases in your own runtime before deploying it.