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

Returns the iterator's current numeric position while consuming heap entries.

The examples focus on the operation itself, including the important distinction: current returns the current heap element instead of its iteration key.

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

SplHeap::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

SplMaxHeap is used because the abstract SplHeap cannot be instantiated. The key call is shown on a small, inspectable dataset.

<?php
$heap = new SplMaxHeap();
$heap->insert(4);
$heap->insert(12);
$heap->insert(7);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

2

Example 2: Checking Behavior

SplMaxHeap is used because the abstract SplHeap cannot be instantiated. The key call is shown on a small, inspectable dataset.

<?php
$heap = new SplMaxHeap();
$heap->insert(2);
$heap->insert(9);
$heap->insert(5);
$heap->insert(1);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

3

Example 3: Practical Example

SplMaxHeap is used because the abstract SplHeap cannot be instantiated. The key call is shown on a small, inspectable dataset.

<?php
$heap = new SplMaxHeap();
$heap->insert(19);
$heap->insert(3);
$heap->insert(11);
$heap->rewind();
echo $heap->key();

Output from a successful local PHP 8.4 run:

2

Important Behavior and Edge Cases

Heap iteration is destructive: advancing removes entries; do not expect array-like stable keys.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Returns the iterator's current numeric position while consuming heap entries.
• Heap iteration is destructive: advancing removes entries; do not expect array-like stable keys.
• current returns the current heap element instead of its iteration key.

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