I'm not sure splitting this to a private provides any benefit, do you?

By doing this, I am getting key validation before returning a generator. Otherwise, you will not get invalid key exception until you call the first iteration

@nicolas-grekas this is about making some logic running before the creation of the generator. If you inline the method, all the code is part of the generator and so runs only when you start iterating. Here, the code before the private method is not part of the generator logic.

Oh ok, of course!

It's possible to do inline function but I thought from code style approach it's not a good way

/**
     * {@inheritdoc}
     */
    public function getItems(array $keys = array())
    {
        foreach ($keys as $key) {
            $this->validateKey($key);
        }

        return (function (array $keys) {
            $f = $this->createCacheItem;
            $now = time();

            foreach ($keys as $key) {
                $isHit = isset($this->expiries[$key]) && ($this->expiries[$key] >= $now || !$this->deleteItem($key));

                yield $key => $f($key, $isHit ? $this->values[$key] : null, $isHit);
            }
        })($keys);
    }

I prefer the private method :)

this is still not inlining the function. It still uses a separate function, even though it is anonymous rather than named.

Sorry for incorrect naming