The feature illustrated below operates on PHP values, objects, or language metadata.
What Is iterator_apply in PHP?
Calls a callback for every element of a Traversable until the callback returns false; the callback must accept any supplied arguments.
iterator_apply(Traversable $iterator, callable $callback, ?array $args = ...) : intParameters:
$iterator— Required. The iterator to attach or traverse.$callback— Required. The callback argument used to configure this operation; its accepted values follow the declared PHP type.$args— Optional. The args argument used to configure this operation; its accepted values follow the declared PHP type.
Return type: int. The callback must return true to continue iteration.
Example 1: Understanding the Basic Behavior
<?php
$iterator = new ArrayIterator([1,2,3]);
$sum = 0;
iterator_apply($iterator, static function () use (&$sum, $iterator): bool { $sum += $iterator->current(); return true; });
echo $sum;Output:
6Explanation: Calls a callback for every element of a Traversable until the callback returns false; the callback must accept any supplied arguments.
Example 2: Testing Another Case
<?php
$iterator = new ArrayIterator(['a','b','c']);
$count = iterator_apply($iterator, static fn(): bool => true);
echo $count;Output:
3Explanation: The callback must return true to continue iteration.
Practical Example: Applying the Operation
<?php
$iterator = new ArrayIterator([2,4,6]);
$seen = [];
iterator_apply($iterator, static function () use ($iterator, &$seen): bool { $seen[] = $iterator->current() * 2; return true; });
print_r($seen);Output:
Array
(
[0] => 4
[1] => 8
[2] => 12
)Explanation: The callback arguments come from the third parameter, not automatically from current iterator values.
Important Behavior and Edge Cases
- The callback must return true to continue iteration.
- The callback arguments come from the third parameter, not automatically from current iterator values.
Comparison With Related Approaches
| Approach | When to Use It |
|---|---|
iterator_apply | Calls a callback for every element of a Traversable until the callback returns false; the callback must accept any supplied arguments. |
foreach | iterator_apply() runs a callback while it returns true; foreach gives direct control over each element and its key. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Forgetting that the callback must return true for iteration to continue. | The callback must return true to continue iteration. |
| Choosing foreach without checking whether it provides the same result. | iterator_apply() runs a callback while it returns true; foreach gives direct control over each element and its key. |
Key Takeaways
- Calls a callback for every element of a Traversable until the callback returns false; the callback must accept any supplied arguments.
- The callback must return true to continue iteration.
- The callback arguments come from the third parameter, not automatically from current iterator values.
The examples demonstrate where iterator_apply fits within php programming. Verify the relevant preconditions whenever you adapt the code to real data.