Null object pattern

[bpolaszek]

Hi there,

I've implemented the Null Object Pattern to allow dynamic strategy assignment (i.e. when your CacheStrategy object comes from dependency injection).

This is simply a NullCacheStrategy object that implements CacheStrategyInterface without actually caching anything. This will help in looking for a valid CacheStrategyInterface without really enabling the cache (for debug purposes, for instance, but there are more use cases).

This pattern has been used in several popular projects, like in PSR-3, symfony/cache, ...

No BC break expected, it's just a new class.

[Kevinrob]

Should it not be false? And same for update?

[bpolaszek]

Hm, when I read PHPdoc's return type hint for CacheStrategyInterface::cache() and CacheStrategyInterface::update(), it's:

/**
* @return bool true if success
*/

So I assumed returning false would mean a failure. However, to my eyes, nothing failed: the NullCacheStrategy accomplished its job with success (i.e. doing nothing).

I feared a further implementation would do this:

if (false === $strategy->cache($request, $response) {
    throw new \RuntimeException("There was an error when trying to cache the request/response");
}

Then, the NullCacheStrategy would systematically fail.

What's your opinion?

[Kevinrob]

However, to my eyes, nothing failed: the NullCacheStrategy accomplished its job with success (i.e. doing nothing).

Yes, you're right. I'm not familiar with this pattern, but I understand it. Thanks for your point of view!