Improvement

[anaelChardan]

Could be nice to have a function like this

    /**
     * Handle a result
     *
     * @param $key
     * @param callable $onSuccess
     * @param callable|null $onError
     *
     * @return mixed
     */
    public function getOrElse($key, callable $onSuccess, callable $onError = null)
    {
        if ($this->containsKey($key)) {
            return $onSuccess($key, $this->get($key));
        }

        return $onError($key);
    }

[Plopix]

I think I am good for that one, @nozavroni might find a better name :)