PHP Iterables

In PHP, an iterable is a data type that can be looped through with a foreach loop or other iteration methods. PHP defines iterables as arrays and objects that implement the Traversable interface.

Here’s a quick rundown of how you can work with iterables in PHP:

Arrays

Arrays are the most common form of iterables in PHP. You can easily loop through them using foreach.

Example:

$fruits = ["apple", "banana", "cherry"];

foreach ($fruits as $fruit) {
    echo $fruit . "\n";
}

Output:

apple
banana
cherry

Objects

To make an object iterable, it must implement the Traversable interface. There are two interfaces that extend Traversable: Iterator and IteratorAggregate.

1. Using Iterator Interface

Implementing the Iterator interface requires defining the following methods: current(), key(), next(), rewind(), and valid().

Example:

class MyIterator implements Iterator {
    private $items = [];
    private $index = 0;

    public function __construct($items) {
        $this->items = $items;
    }

    public function current() {
        return $this->items[$this->index];
    }

    public function key() {
        return $this->index;
    }

    public function next() {
        ++$this->index;
    }

    public function rewind() {
        $this->index = 0;
    }

    public function valid() {
        return isset($this->items[$this->index]);
    }
}

$iterator = new MyIterator(["apple", "banana", "cherry"]);

foreach ($iterator as $fruit) {
    echo $fruit . "\n";
}

Output:

apple
banana
cherry

2. Using IteratorAggregate Interface

IteratorAggregate is a simpler way to make an object iterable. You only need to implement the getIterator() method which should return an instance of Traversable (like an ArrayIterator).

Example:

class MyIterable implements IteratorAggregate {
    private $items = [];

    public function __construct($items) {
        $this->items = $items;
    }

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

$iterable = new MyIterable(["apple", "banana", "cherry"]);

foreach ($iterable as $fruit) {
    echo $fruit . "\n";
}

Output:

apple
banana
cherry

Conclusion

In summary, PHP iterables can be arrays or objects that implement the Traversable interface. Arrays are the simplest form, but you can also create custom iterable objects by implementing Iterator or IteratorAggregate. This flexibility allows you to control how objects are iterated over, making PHP a powerful language for handling different types of data collections.