blackhole cache storage adapter

[marc-mabe]

This PR implements a black hole storage adapter (like in #4196) but doesn't extends AbstractAdapter so there is no overhead and it implements all interfaces to make it possible as a replacement in all cases.

Because it doesn't extend AbstractAdapter it has no plugin system implemented and configuring plugins together with this adapter will result in an exception.

[prolic]

Just curious: How to use the blackhole adapter, when I need plugins in a real world application. How can I replace this with a blackhole adapter?

[marc-mabe]

@prolic What do you mean with "I need plugins"? Plugins exists to add functionalities (like the Serializer) or to influence behavior of a storage (like the ExceptionHandler). The plugin system isn't part of the storage interface as plugins doesn't change basics of a key-value storage.

Applications should depend of a public (and well defined) API which will be the case here. If there is a very special case your application requires a behavior you should use the Capabilities of the storage to know if that storage will be ok. If the BlackHole storage will not you have to write your own. If you have a behavior not listed within the Capabilities you should create an issue.

... you need do remove the plugins - key of your configuration to instantiate the black hole storage using the factory.

[prolic]

Thanks for your explanations.

[weierophinney]

change to @return self