Add ArrayObject::isAssoc()

[leocavalcante]

Checks whether the given array wrapped by ArrayObject is associative (uses string keys like a hashmap).

[deminy]

The Swoole team had discussed the implementations of this particular method two months ago. It's always inefficient when implemented in PHP, like the one implemented in Laravel ( https://github.com/laravel/framework/blob/v8.9.0/src/Illuminate/Collections/Arr.php#L389 ). Although there were thoughts like comparing keys in reverse order, it doesn't help much in worse cases.

Let's see how others think. Thanks @leocavalcante for the PRs!

[twose]

The best way is php/php-src#6070

$index = count($array);
reverse_foreach($array as $key => void) {
    if ($key !== --$index) {
        return false;
    }
    return true;
}

[deminy]

According to this PHP RFC (Add array_is_list(array $array): bool), a new PHP function array_is_list() will be added to PHP 8.1. This new function can be found in the Docker image for PHP nightly (8.1-dev only):

docker run --rm -ti phpdaily/php:8.1-dev php -r 'echo function_exists("array_is_list") ? "yes" : "no", "\n";'

As discussed, the same function written in PHP is much less efficient compared to a built-in PHP function like array_is_list(). Thus, we prefer not to add method ArrayObject::isAssoc() to the Swoole library; developers can add and use this method (or some variations) manually in their projects when needed.

Thanks again to @leocavalcante for submitting the PR and for contributing to the open source community!