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

Returns and removes the entry with the greatest priority.

The examples focus on the operation itself, including the important distinction: top inspects the highest-priority entry without removing it.

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::extract()

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

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The extract call is shown on a small, inspectable dataset.

<?php
$heap = new SplPriorityQueue();
$heap->insert('task-4', 4);
$heap->insert('task-12', 12);
$heap->insert('task-7', 7);
echo json_encode($heap->extract());
echo " remaining=" . count($heap);

Output from a successful local PHP 8.4 run:

"task-12" remaining=2

Example 2: Checking Behavior

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The extract call is shown on a small, inspectable dataset.

<?php
$heap = new SplPriorityQueue();
$heap->insert('task-2', 2);
$heap->insert('task-9', 9);
$heap->insert('task-5', 5);
$heap->insert('task-1', 1);
echo json_encode($heap->extract());
echo " remaining=" . count($heap);

Output from a successful local PHP 8.4 run:

"task-9" remaining=3

Example 3: Practical Example

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The extract call is shown on a small, inspectable dataset.

<?php
$heap = new SplPriorityQueue();
$heap->insert('task-19', 19);
$heap->insert('task-3', 3);
$heap->insert('task-11', 11);
echo json_encode($heap->extract());
echo " remaining=" . count($heap);

Output from a successful local PHP 8.4 run:

"task-19" remaining=2

Important Behavior and Edge Cases

Values with equal priorities have unspecified relative order.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Returns and removes the entry with the greatest priority.
• Values with equal priorities have unspecified relative order.
• top inspects the highest-priority entry without removing it.

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