Fix regression with using acts_as_list on base classes

[botandrose]

#123 introduced a regression, since acts_as_list_class now returns the subclass, not the superclass. My use-case is as follows:

class Segment < AR::Base
  acts_as_list
end

class Video < Segment; end
class Quiz < Segment; end
class Exam < Segment; end

The application is an online course, which is composed of videos, quizzes, and exams. acts_as_list keeps these in order. However, after #123, lower_item will return the next item of the same subclass, skipping over other segments of other subclasses, which is not at all desired.

If one desires this behavior, declaring acts_as_list on the subclasses separately makes sense. This PR reverts the regression, and includes tests for both use-cases.

[swanandp]

@botandrose We want to support Rubinius as well, but the issue is about bundler and rbx versioning, so I'll let it slide for now.

[botandrose]

Thank you for the quick response! <3

[severin]

Thanks for fixing this! Just ran into the same issue.

[bolshakov]

Could you please explain what does this string mean?

[botandrose]

Sure! There's a lot going on in this little change, can you be a little more specific with your question? Are you asking about the change from self.class to self.name, or are you asking about the syntax madness of ::#{}?

[bolshakov]

I'm asking about syntax madness.

[botandrose]

Ah, yeah. So there are two things going on there.

One is that we're inside a class_eval metaprogramming block, so any string interpolation with #{} gets applied directly to the ruby code being constructed. So if the value of self.name is "TheBaseClass" when the acts_as_list macro is invoked, that line compiles to ::TheBaseClass.

Second is ::, which is the scope resolution operator. This is there to make sure that we are definitely getting the "root-level" TheBaseClass, instead of unintentionally getting something like SomeOtherModuleThatAlsoContains::TheBaseClass.

Does this help?

[bolshakov]

Yes this is very helpful! I've missed that it happens inside the string!
Thank you!