On 23 Dec 2008, at 18:26, Sarah Allen wrote:
Matt Wynne wrote:
ActiveRecord::Validations uses a trick that's used widely in rails,
and is arguably[1] becoming a Ruby idiom, apparently.
This is the interesting bit, around line #275:
def self.included(base) # :nodoc:
base.extend ClassMethods
So basically that means that when the class ActiveRecord::Base
includes the module ActiveRecord::Validations, that module extends
the
thing which included it (in this case ActiveRecord::Base) with the
class methods defined in ActiveRecords::Validations::ClassMethods.
Does that make sense?
um, no. You say that the class ActiveRecord::Base includes the module
ActiveRecord::Validations, but I don't see that in the code I'm
looking
at here:
http://dev.rubyonrails.org/browser/branches/2-0-stable/activerecord/lib/active_record/base.rb
Try here:
http://dev.rubyonrails.org/browser/branches/2-0-stable/activerecord/lib/active_record.rb
On line 42: require 'active_record/validations'
If I assume that I'm looking at the wrong code or it happens thru some
magic then you can make a module which will add its class methods to
the
class which includes it?
I believe that's how modules work, but it's not by magic. If I'm
reading this Ruby book (by the Pragmatic Programmer's) here correctly
then Ruby creates a singleton class of the object calling extend
(which I think is the reasoning behind the code referenced by Matt),
then includes the module into that singleton class, which adds the
instance methods of the module into the superclass chain for that
object's class.
Is that some kind of trick to create multiple
inheritance? Is there any way without digging thru source to know
which
class include methods from other classes or do y'all just get so cozy
with every Rails class you use that you "just know?"
The Ruby classes Module and Object have some methods to determine
other included modules, available public|private|protected methods,
etc. if that helps.
Perhaps someone more experienced can fill in any gaps I may've missed
- just happened to be reading about this myself...
Jeremiah
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