Using Iterables

Iterable can be used as a parameter type to indicate that a function requires a set of values, but does not care about the form of the value set since it will be used with foreach. If a value is not an array or instance of Traversable, a TypeError will be thrown.

<?php

function foo(iterable $iterable) {
    foreach ($iterable as $value) {
        // ...
    } 
}

?>

Parameters declared as iterable may use null or an array as a default value.

<?php

function foo(iterable $iterable = []) {
    // ...
}

?>

Iterable can also be used as a return type to indicate a function will return an iterable value. If the returned value is not an array or instance of Traversable, a TypeError will be thrown.

<?php

function bar(): iterable {
    return [1, 2, 3];
}

?>

Functions declaring iterable as a return type may also be generators.

<?php

function gen(): iterable {
    yield 1;
    yield 2;
    yield 3;
}

?>

Iterable Type Variance

Classes extending/implementing may broaden methods using array or Traversable as parameter types to iterable or narrow return types from iterable to array or Traversable.

<?php

interface Example {
    public function method(array $array): iterable;
}

class ExampleImplementation implements Example {
    public function method(iterable $iterable): array {
        // Parameter broadened and return type narrowed.
    }
}

?>