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

Compares two priority values to determine their ordering within the maximum-priority heap.

The examples focus on the operation itself, including the important distinction: insert accepts both a value and its priority; compare orders only priorities.

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::compare(mixed $priority1, mixed $priority2)

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.

Parameters

• priority1: required.
• priority2: required.

Example 1: Basic Use

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The compare 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 $heap->compare(20, 5);

Output from a successful local PHP 8.4 run:

1

Example 2: Checking Behavior

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The compare 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 $heap->compare(20, 5);

Output from a successful local PHP 8.4 run:

1

Example 3: Practical Example

The queue is a max-priority queue; equal priorities have no guaranteed FIFO order. The compare 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 $heap->compare(20, 5);

Output from a successful local PHP 8.4 run:

1

Important Behavior and Edge Cases

Equal priorities have unspecified extraction order; do not assume stable FIFO ties.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Compares two priority values to determine their ordering within the maximum-priority heap.
• Equal priorities have unspecified extraction order; do not assume stable FIFO ties.
• insert accepts both a value and its priority; compare orders only priorities.

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