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

Changes FIFO/LIFO traversal and KEEP/DELETE behavior with a combined bitmask.

The examples focus on the operation itself, including the important distinction: getIteratorMode reports the current bitmask.

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::setIteratorMode(int $mode)

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

• mode: required.

Example 1: Basic Use

The list begins with 3 values. Notice how setIteratorMode 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');
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_KEEP);
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

{"2":"water","1":"coffee","0":"tea"}

Example 2: Checking Behavior

The list begins with 4 values. Notice how setIteratorMode 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');
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_KEEP);
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

{"3":"four","2":"three","1":"two","0":"one"}

Example 3: Practical Example

The list begins with 3 values. Notice how setIteratorMode 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);
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_KEEP);
echo json_encode(iterator_to_array($list));

Output from a successful local PHP 8.4 run:

{"2":12,"1":8,"0":4}

Important Behavior and Edge Cases

DELETE iteration consumes values; choose KEEP to retain entries.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Changes FIFO/LIFO traversal and KEEP/DELETE behavior with a combined bitmask.
• DELETE iteration consumes values; choose KEEP to retain entries.
• getIteratorMode reports the current bitmask.

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