As of PHP 7.1, you can now type hint your method/function arguments with the keyword iterable for handling arrays or even objects that implement the Traversable interface.

Let’s create an example where we can convert any string to a slug. We’ll have 2 methods so that we can pass either a string or iterable data.

We’ll start by setting up our SlugGenerator class.

<?php

class SlugGenerator
{
    public static function byArray(iterable $data)
    {
        $results = [];

        foreach($data as $name) {
            $results[] = self::byString($name);
        }

        return $results;
    }

    public static function byString(string $name)
    {
        $slug = preg_replace('/[^A-Za-z0-9-]+/', '-', $name);
        $slug = strtolower($slug);

        return $slug;
    }
}

For our first example on using the above we’ll use a simple array.

<?php

$titles = [
    'My Test Title 1',
    'My Test Title 2',
    'My Test Title 3',
];

$slugs = SlugGenerator::byArray($titles); // Outputs array of slugs

Now let’s setup an example by passing a traversable object.

<?php

class Titles implements IteratorAggregate
{
    private $titles = [];

    public function add(string $title)
    {
        array_push($this->titles, $title);
    }

    public function getIterator()
    {
        return new ArrayIterator($this->titles);
    }
}

$titles = new Titles;
$titles->add('Test Title 1');
$titles->add('Test Title 2');
$titles->add('Test Title 3');

$slugs = SlugGenerator::byArray($titles); // Outputs array of slugs

You'll see that we’re able to use the same SlugGenerator class without having to modify our original class. Awesome, right?