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

Removes and returns the first entry of the list.

The examples focus on the operation itself, including the important distinction: pop removes from the end instead of the beginning.

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::shift()

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 shift changes or observes its indexed deque rather than an ordinary associative array.

<?php
$list = new SplDoublyLinkedList();
$list->push('tea');
$list->push('coffee');
$list->push('water');
echo json_encode($list->shift());
echo " remaining=" . count($list);

Output from a successful local PHP 8.4 run:

"tea" remaining=2

Example 2: Checking Behavior

The list begins with 4 values. Notice how shift 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');
$list->push('four');
echo json_encode($list->shift());
echo " remaining=" . count($list);

Output from a successful local PHP 8.4 run:

"one" remaining=3

Example 3: Practical Example

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

<?php
$list = new SplDoublyLinkedList();
$list->push(4);
$list->push(8);
$list->push(12);
echo json_encode($list->shift());
echo " remaining=" . count($list);

Output from a successful local PHP 8.4 run:

4 remaining=2

Important Behavior and Edge Cases

An empty list raises RuntimeException.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Removes and returns the first entry of the list.
• An empty list raises RuntimeException.
• pop removes from the end instead of the beginning.

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