Advanced typed array types

With modern PHP tooling, not only we can do @param array<Type> $value but a lot more.

We can specify literal keys:

/**
 * @param array{begin: int, interval: int} $data
 *
 * @return int
 */
function transform(array $data): int
{
    return $data['begin'] + $data['interval'];
}

The notation for arrays is array<KeyType, ValueType>. If we only pass one type, it is the type of the value.

We can even go as far as to specify the array should not be empty:

/**
 * @param non-emptyarray<string, mixed> $data
 *
 * @return non-empty-string
 */
function concatKeys(array $data): string
{
    $output = '';

    foreach($data as $key => $v) {
        $output .= $key;
    }

    return $output;
}

Source