MultipleIterator combines values from multiple iterators at matching iteration positions.
What Is MultipleIterator::valid in PHP?
Checks whether the current traversal position still contains an element.
MultipleIterator::valid()This operation does not accept method arguments.
Example 1: Understanding the Basic Behavior
<?php
$iterator = new MultipleIterator(MultipleIterator::MIT_NEED_ANY);
$firstIterator = new ArrayIterator([1, 2]);
$secondIterator = new ArrayIterator(['a', 'b']);
$iterator->attachIterator($firstIterator, "numbers");
$iterator->attachIterator($secondIterator, "letters");
$iterator->rewind();
var_dump($iterator->valid());Output:
bool(true)Explanation: Checks whether the current traversal position still contains an element.
Example 2: Testing Another Case
<?php
$iterator = new MultipleIterator(MultipleIterator::MIT_NEED_ANY);
$firstIterator = new ArrayIterator([5, 6]);
$secondIterator = new ArrayIterator(['c', 'd']);
$iterator->attachIterator($firstIterator, "numbers");
$iterator->attachIterator($secondIterator, "letters");
$iterator->rewind();
var_dump($iterator->valid());Output:
bool(true)Explanation: The result describes the current cursor state, not whether the entire collection is non-empty.
Practical Example: Applying the Operation
<?php
$iterator = new MultipleIterator(MultipleIterator::MIT_NEED_ANY);
$firstIterator = new ArrayIterator([8, 9]);
$secondIterator = new ArrayIterator(['e', 'f']);
$iterator->attachIterator($firstIterator, "numbers");
$iterator->attachIterator($secondIterator, "letters");
$iterator->rewind();
var_dump($iterator->valid());Output:
bool(true)Explanation: The MIT_NEED_ALL and MIT_NEED_ANY options change when iteration stops; keys may be positional or associated.
Important Behavior and Edge Cases
- The result describes the current cursor state, not whether the entire collection is non-empty.
- The MIT_NEED_ALL and MIT_NEED_ANY options change when iteration stops; keys may be positional or associated.
Comparison With Related Approaches
| Approach | When to Use It |
|---|---|
MultipleIterator::valid | Checks whether the current traversal position still contains an element. |
ArrayIterator | AppendIterator concatenates iterators sequentially; MultipleIterator reads several iterators in parallel. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Using valid() to count items instead of checking the current cursor. | The result describes the current cursor state, not whether the entire collection is non-empty. |
| Choosing ArrayIterator without checking whether it provides the same result. | AppendIterator concatenates iterators sequentially; MultipleIterator reads several iterators in parallel. |
Key Takeaways
- Checks whether the current traversal position still contains an element.
- The result describes the current cursor state, not whether the entire collection is non-empty.
- The MIT_NEED_ALL and MIT_NEED_ANY options change when iteration stops; keys may be positional or associated.
The examples demonstrate where MultipleIterator::valid fits within synchronized iteration. Verify the relevant preconditions whenever you adapt the code to real data.