PHP iterator_apply() Function

The iterator_apply() function is an inbuilt function in PHP that is used to apply a user-defined callback function to each element of an iterator. It allows you to iterate any element without using any kind of loop.

Syntax:

int iterator_apply(
    Traversable $iterator, 
    callable $callback, 
    ?array $args = nul
l): int

Parameters: This function accepts three parameters that are described below.

• $iterator: The iterator on which the callback function will be applied
• $funtion: This is the callback function. That is to call every single element. It must be returned ‘true’ for further calling.
• $args: An array of arguments; each element of args is passed to the callback callback as a separate argument.

Return Values: The iterator_apply() function returns the iterator element.

Program 1: The following program demonstrates the iterator_apply() function.

PHP

<?php

function check_for_a(Iterator $iterator) {
    $element = $iterator->current();

    if (stripos($element, 'a') !== false) {
        echo "Element '$element' " .
            "contains the letter 'a'.\n";
    } else {
        echo "Element '$element' " .
            "does not contain the letter 'a'.\n";
    }

    return TRUE;
}

$fruits = array(
    "Orange",
    "Banana",
    "Grapes",
    "Kiwi"
);

$arrIter = new ArrayIterator($fruits);

iterator_apply($arrIter,
    "check_for_a", array($arrIter));

?>

Output

Element 'Orange' contains the letter 'a'.
Element 'Banana' contains the letter 'a'.
Element 'Grapes' contains the letter 'a'.
Element 'Kiwi' does not contain the letter 'a'.

Program 2: The following program demonstrates the iterator_apply() function.

PHP

<?php

function print_positive_integers(Iterator $iterator) {
    $element = $iterator->current();

    if (is_int($element) && $element > 0) {
        echo "Positive Integer: $element\n";
    }
    return TRUE;
}

$arr = array(10, -5, 20, -15, 30, 0, 25, -8, 40);

$arrIter = new ArrayIterator($arr);

iterator_apply(
    $arrIter,
    "print_positive_integers",
    array($arrIter)
);

?>

Output

Positive Integer: 10
Positive Integer: 20
Positive Integer: 30
Positive Integer: 25
Positive Integer: 40

Reference: https://www.php.net/manual/en/function.iterator-apply.php