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

Returns the final list value without removing it.

The examples focus on the operation itself, including the important distinction: pop removes the last value while returning it.

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::top()

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 top 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->top());

Output from a successful local PHP 8.4 run:

"water"

Example 2: Checking Behavior

The list begins with 4 values. Notice how top 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->top());

Output from a successful local PHP 8.4 run:

"four"

Example 3: Practical Example

The list begins with 3 values. Notice how top 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->top());

Output from a successful local PHP 8.4 run:

12

Important Behavior and Edge Cases

Do not call on an empty list; unlike pop, top leaves the list unchanged.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Returns the final list value without removing it.
• Do not call on an empty list; unlike pop, top leaves the list unchanged.
• pop removes the last value while returning it.

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