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

Reports the numeric position of the current iterator entry.

The examples focus on the operation itself, including the important distinction: current returns the entry value instead of its position.

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

SplDoublyLinkedList::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 list begins with 3 values. Notice how key changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push('tea');
$list->push('coffee');
$list->push('water');
$list->rewind();
$list->next();
echo $list->key();

Output from a successful local PHP 8.4 run:

1

Example 2: Checking Behavior

The list begins with 4 values. Notice how key changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push('one');
$list->push('two');
$list->push('three');
$list->push('four');
$list->rewind();
$list->next();
echo $list->key();

Output from a successful local PHP 8.4 run:

1

Example 3: Practical Example

The list begins with 3 values. Notice how key changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push(4);
$list->push(8);
$list->push(12);
$list->rewind();
$list->next();
echo $list->key();

Output from a successful local PHP 8.4 run:

1

Important Behavior and Edge Cases

The key depends on the current cursor and iteration direction.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Reports the numeric position of the current iterator entry.
• The key depends on the current cursor and iteration direction.
• current returns the entry value instead of its position.

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