PHP MultipleIterator::attachIterator() Method: Usage and Examples

MultipleIterator combines values from multiple iterators at matching iteration positions.

What Is MultipleIterator::attachIterator in PHP?

Adds an iterator to a MultipleIterator so its values can be traversed alongside others.

MultipleIterator::attachIterator(Iterator $iterator, string|int|null $info = ...)

Parameters:

• $iterator — Required. The iterator to attach or traverse.
• $info — Optional. The info argument used to configure this operation; its accepted values follow the declared PHP type.

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");
$thirdIterator = new ArrayIterator([true, false]);
$iterator->attachIterator($thirdIterator, "flags");
var_dump($iterator->countIterators());

Output:

int(3)

Explanation: Adds an iterator to a MultipleIterator so its values can be traversed alongside others.

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");
$thirdIterator = new ArrayIterator([true, false]);
$iterator->attachIterator($thirdIterator, "flags");
var_dump($iterator->countIterators());

Output:

int(3)

Explanation: Attached iterators advance together; adding a source does not concatenate values.

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");
$thirdIterator = new ArrayIterator([true, false]);
$iterator->attachIterator($thirdIterator, "flags");
var_dump($iterator->countIterators());

Output:

int(3)

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

• Attached iterators advance together; adding a source does not concatenate values.
• The MIT_NEED_ALL and MIT_NEED_ANY options change when iteration stops; keys may be positional or associated.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Adds an iterator to a MultipleIterator so its values can be traversed alongside others.
• Attached iterators advance together; adding a source does not concatenate values.
• The MIT_NEED_ALL and MIT_NEED_ANY options change when iteration stops; keys may be positional or associated.

The examples demonstrate where MultipleIterator::attachIterator fits within synchronized iteration. Verify the relevant preconditions whenever you adapt the code to real data.