Hi all!
As discussed at the MediaWiki Architecture session at Wikimania, I have created an RFC for the TitleValue class, which could be used to replace the heavy-weight Title class in many places. The idea is to show case the advantages (and difficulties) of using true "value objects" as opposed to "active records". The idea being that hair should not know how to cut itself.
You can find the proposal here: https://www.mediawiki.org/wiki/Requests_for_comment/TitleValue
Any feedback would be greatly appreciated.
-- daniel
PS: I have included the some parts of the proposal below, to give a quick impression.
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== Motivation ==
The old Title class is huge and has many dependencies. It relies on global state for things like namespace resolution and permission checks. It requires a database connection for caching.
This makes it hard to use Title objects in a different context, such as unit tests. Which in turn makes it quite difficult to write any clean unit tests (not using any global state) for MediaWiki since Title objects are required as parameters by many classes.
In a more fundamental sense, the fact that Title has so many dependencies, and everything that uses a Title object inherits all of these dependencies, means that the MediaWiki codebase as a whole has highly "tangled" dependencies, and it is very hard to use individual classes separately.
Instead of trying to refactor and redefine the Title class, this proposal suggest to introduce an alternative class that can be used instead of Title object to represent the title of a wiki page. The implementation of the old Title class should be changed to rely on the new code where possible, but its interface and behavior should not change.
== Architecture ==
The proposed architecture consists of three parts, initially:
# The TitleValue class itself. As a value object, this has no knowledge about namespaces, permissions, etc. It does not support normalization either, since that would require knowledge about the local configuration.
# A TitleParser service that has configuration knowledge about namespaces and normalization rules. Any class that needs to turn a string into a TitleValue should require a TitleParser service as a constructor argument (dependency injection). Should that not be possible, a TitleParser can be obtained from a global registry.
# A TitleFormatter service that has configuration knowledge about namespaces and normalization rules. Any class that needs to turn a TitleValue into a string should require a TitleFormatter service as a constructor argument (dependency injection). Should that not be possible, a TitleFormatter can be obtained from a global registry.