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

Returns the numeric iterator index of the current priority queue item.

The examples focus on the operation itself, including the important distinction: current returns data or priority according to the chosen extraction mode.

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::key()

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 key 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);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

2

Example 2: Checking Behavior

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The key 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);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

3

Example 3: Practical Example

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The key 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);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

2

Important Behavior and Edge Cases

This is not the priority value; use EXTR_PRIORITY to retrieve priorities.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Returns the numeric iterator index of the current priority queue item.
• This is not the priority value; use EXTR_PRIORITY to retrieve priorities.
• current returns data or priority according to the chosen extraction mode.

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