Wednesday, 12 August 2009

Musings on a Moose

come to sweden, see the majestic moose (paraphrased from Monty Python and the Holy Grail).

I am starting to look at Moose as an alternative to Class::Std and other modules for OO Perl. It has very good support from the community, and looks to be fast becoming the framework of choice.

I will start off by saying I like it. The setup of my::module is very easy, and reads very cleanly. I like the declaration of variable types on the accessors, and it obvious when an attribute is needed on new, (just set 'required' flag). I especially like the ability to make an attribute ro.

However, that leads me to a small bugbear I have. I have mentioned before about encapsulation, Class::Std objects are blessed scalars, and as such can't have keys. Your attributes are set up as keys on internal hashes, and as such can only be exposed via a method.

The Moose object created is a blessed hash, and, the attributes are stored in keys. This means that your user can still override the ro attribute by just using the key. Encapsulation is broken.

Someone in my office used a good simile here, which I think he attributed to Larry Wall, which is:

"Your neighbour stays out of your garden, because it is the right thing to do, not because you have a shotgun."

That might be the case, but I'd rather enforce the use of accessors from the start than run the risk of user's using the key. However, I plan to try out MooseX::InsideOut to see if this can enforce this once I'm more tightly used to the basics.

Another thing I find very good are the additional modifiers for the accessors. We have found that making use of predicates and lazy_build really improves the code layout and speed of object creation.

I have now been building the pluggable pipeline project using Moose, and it has been very quick to build the objects and code. I would say that I think once upto speed, and once I have tested out MooseX::InsideOut, I think that development time of code should reduce by about 10% and code maintainability should go up about 25%.

So a big thumbs up from myself, and my development team also. Whilst I think at the moment there would be no plans to convert our ClearPress based apps to Moose, I think I'm tempted to try to switch my Class::Std modules, and certainly all new projects will go that way.

Big Thanks to all the people who work on Moose. Is there a book in the works? I for one would get it, I'd even contribute if you'd like.


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Stevan Little said...

Regarding a Moose book, we do not have anything in the works currently but Leon (Acme) Brocard has typeset the documentation and uploaded it to Lulu here (