Class#subclasses

rubyonrails-core
1

I am writing the AS core extensions guide, and would like to know your opinion about Class#subclasses:

AS defines Class#subclasses, it returns the name of all descendants (strings). Same as AC::Base.subclasses.

AR::Base.subclasses on the other hand returns all descendants (classes), and it is protected.

The guide could warn about AR::Base. We could also redefine AR::Base.subclasses to match the rest (I'd volunteer). ack says there are not a lot of occurrences, but it wouldn't be backwards compatible.

What do you think?

2

I can imagine that plugins might use Base.subclasses to iterate over AR models.

thinking-sphinx does this, for instance.

The question is, why would we standardize on strings? Why not actual references, like ancestors?

3

I first thought about changing AR because at least that is a protected method and it could be the case that it breaks less code.

But all being equal, I'd expect subclasses to return class objects indeed, for example Object#subclasses_of does, and anyway that is what the name would suggest to me.

4

Ah, but they are not equivalent because AC::Base#subclasses includes names of non-reachable class objects, whereas Class#subclasses filters them out.

5

Ah, but they are not equivalent because AC::Base#subclasses includes names of non-reachable class objects, whereas Class#subclasses filters them out.

This difference is probably just to enable reset_subclasses to work around the ruby memory-leak discussed at length on:

http://rails.lighthouseapp.com/projects/8994/tickets/1339-arbase-should-not-be-nuking-its-children-just-because-it-lost-interest

There's no reason that the AR version can't be called something else and move subclasses to be the same everywhere.

6

I've seen that the classes in the framework that need #subclasses implement their own version using the inherited hook.

It turns out that Class#subclasses was not being used in the framework, Jeremy suggested it shouldn't be a core extension in that case and we've removed it.

That in turn unrolled a series of related utilities that were unused, they are:

   Object#subclasses_of    Object#remove_subclasses_of    Object#extended_by    Object#extend_with_included_modules_from    Class#remove_subclasses    Class#remove_class    Class#reachable?    Class#descedents

They are gone as well, and I'll prepare a patch to deprecate them for 2.3.

7

Looks like remnants of the old reloading system?

So, if some classes (like ActiveRecord) in the framework implement their own subclasses, why not implement it once in AS and remove those other implementations?

8

Sounds good because there are 4 o 5 of them. I think they are equivalent except perhaps for visibility which is not probably big deal if we uniform this. I'll have a look at it.