ArrayAccess

ArrayAccess is an interface that allows objects to be accessed like arrays using square brackets, similar to accessing elements in a regular array. When a class implements the ArrayAccess interface, it must provide methods to define how the object behaves when accessed like an array.

• offsetExists($offset): this method is called to check if a specific offset exists in the object. It should return a boolean value: true if the offset exists, false otherwise.

• offsetGet($offset): this method is called to try to retrieve the value associated with a specific offset. It should return the value at that offset.

• offsetSet($offset, $value): this method is called to try to set a value for a specific offset. It takes two parameters: the offset and the value to be set.

• offsetUnset($offset): this method is called to unset or remove a value associated with a specific offset.

Implementing ArrayAccess can be useful to create custom data structures or objects that mimic array behavior, providing a convenient and consistent way to work with data.

ArrayAccess is often complemented with Countable, to make the object yet even more like an array.

<?php

class LimitedArray implements ArrayAccess {
    public $a = 1;
    public $b = 1;
    public $c = 1;

    public function offsetSet($offset, $value): void {
        if (in_array($offset, ['a', 'b', 'c'])) {
            $this->$offset = $value;
        }
        // else ignore
    }

    public function offsetExists($offset): bool {
        return in_array($offset, ['a', 'b', 'c']);
    }

    public function offsetUnset($offset): void {
        // do nothing
    }

    public function offsetGet($offset): mixed {
        if (in_array($offset, ['a', 'b', 'c'])) {
            return $this->$offset;
        }
    }
}

$limitedArray = new LimitedArray();

$limitedArray['a'] = 3;
$limitedArray['d'] = 13;

echo $limitedArray['a']; // 3
echo $limitedArray['d']; // null

?>

Documentation

Related : Countable Interface, Iterable, Associative Array, PHP Native Interfaces