PHP SplDoublyLinkedList unshift() Function

The SplDoublyLinkedList::unshift() function is an inbuilt function in PHP which is used to add the element at the beginning of a doubly linked list.

Syntax:

void SplDoublyLinkedList::unshift( $value )

Parameters: This function accepts a single parameter $value which is used to unshift the value in a doubly linked list.

Return Value: It does not return any value.

Below programs illustrate the SplDoublyLinkedList::unshift() function in PHP:

Program 1:

<?php

// Declare an empty SplDoublyLinkedList
$list = new \SplDoublyLinkedList;

// Use SplDoublyLinkedList::add() function to
// add elements to the SplDoublyLinkedList
$list->add(0, 30);
$list->add(1, 20);
$list->add(2, 30);
$list->add(3, "Geeks");
$list->add(4, 'G');

// Use unshift() function
$list->unshift("GeeksforGeeks");

// Display the list elements
print_r($list);

?>

Output:

SplDoublyLinkedList Object
(
    [flags:SplDoublyLinkedList:private] => 0
    [dllist:SplDoublyLinkedList:private] => Array
        (
            [0] => GeeksforGeeks
            [1] => 30
            [2] => 20
            [3] => 30
            [4] => Geeks
            [5] => G
        )

)

Program 2:

<?php

// Declare an empty SplDoublyLinkedList
$list = new \SplDoublyLinkedList();

// Use SplDoublyLinkedList::push() function to
// add elements to the SplDoublyLinkedList
$list->push(1);
$list->push(2);
$list->push(3);
$list->push(8);
$list->push(5);

// Use unshift() function
$list->unshift("Geeks");

// Display the list elements
print_r($list);

?>

Output:

SplDoublyLinkedList Object
(
    [flags:SplDoublyLinkedList:private] => 0
    [dllist:SplDoublyLinkedList:private] => Array
        (
            [0] => Geeks
            [1] => 1
            [2] => 2
            [3] => 3
            [4] => 8
            [5] => 5
        )

)

Reference: https://www.php.net/manual/en/spldoublylinkedlist.unshift.php