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

Reports whether the iterator cursor currently points to an entry.

The examples focus on the operation itself, including the important distinction: isEmpty checks the collection, not the cursor's current 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::valid()

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 valid 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->rewind();
echo $list->valid() ? "valid" : "invalid";

Output from a successful local PHP 8.4 run:

valid

Example 2: Checking Behavior

The list begins with 4 values. Notice how valid 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->rewind();
echo $list->valid() ? "valid" : "invalid";

Output from a successful local PHP 8.4 run:

valid

Example 3: Practical Example

The list begins with 3 values. Notice how valid 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->rewind();
echo $list->valid() ? "valid" : "invalid";

Output from a successful local PHP 8.4 run:

valid

Important Behavior and Edge Cases

The result becomes false after moving past the traversal boundary.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Reports whether the iterator cursor currently points to an entry.
• The result becomes false after moving past the traversal boundary.
• isEmpty checks the collection, not the cursor's current position.

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