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

Inserts a value at a specified zero-based position, shifting later elements toward the end.

The examples focus on the operation itself, including the important distinction: push appends; add inserts at a specified 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::add(int $index, mixed $value)

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

• index: required.
• value: required.

Example 1: Basic Use

The list begins with 3 values. Notice how add 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');
$list->add(1, 'milk');
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

["tea","milk","coffee","water"]

Example 2: Checking Behavior

The list begins with 4 values. Notice how add 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');
$list->add(1, 'extra');
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

["one","extra","two","three","four"]

Example 3: Practical Example

The list begins with 3 values. Notice how add 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);
$list->add(2, 10);
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

[4,8,10,12]

Important Behavior and Edge Cases

An out-of-range index raises OutOfRangeException; use push to append at the end.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Inserts a value at a specified zero-based position, shifting later elements toward the end.
• An out-of-range index raises OutOfRangeException; use push to append at the end.
• push appends; add inserts at a specified position.

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