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

Moves the iterator backward relative to its current traversal direction.

The examples focus on the operation itself, including the important distinction: next moves in the forward iterator direction.

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::prev()

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 prev 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();
$list->prev();
echo json_encode($list->current());

Output from a successful local PHP 8.4 run:

"tea"

Example 2: Checking Behavior

The list begins with 4 values. Notice how prev 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();
$list->prev();
echo json_encode($list->current());

Output from a successful local PHP 8.4 run:

"one"

Example 3: Practical Example

The list begins with 3 values. Notice how prev 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();
$list->prev();
echo json_encode($list->current());

Output from a successful local PHP 8.4 run:

4

Important Behavior and Edge Cases

For meaningful results, first move the cursor away from the initial position.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Moves the iterator backward relative to its current traversal direction.
• For meaningful results, first move the cursor away from the initial position.
• next moves in the forward iterator direction.

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