From: Francis Cianfrocca <garbagecat10@...>
Date: 2006-05-23T01:23:05+09:00
Subject: Re: initializing instance variables in a module

Jeff, I tried a few combinations of class_eval and module_eval and I
couldn't figure it out. What seems to be desired is for the mixed-in
module code to create an instance variable in the class which is doing
the mixin. I'll bet there's a way to do it.

On 5/22/06, Jeff Rose <rosejn@gmail.com> wrote:
> That's what I was afraid of.  In this example case it's no big deal, but
> in a module where you are accessing a more complex variable many times
> it's a real pain, let alone inefficient.  We are working on an event
> system, so the hash is a hash of arrays or possibly a hash of hashes.
> Any of 4 methods could be called, which would require an initialized
> value.  Having this in every method is sorta lame...
>
>    handlers = (@event_handlers ||= Hash.new {|k,v| k[v] = []})[key]
>
> Of course we can pull it out to a method:
>
> def handlers(key)
>    @event_handlers ||= Hash.new {|k,v| k[v] = []})[key]
> end
>
>   but just initializing on inclusion seems to be the most reasonable
> way, doesn't it?
>
> -Jeff
>
> Ryan Leavengood wrote:
> > module Foo
> >   def add_stuff(key, stuff)
> >     (@foo_the_stuff ||= {})[key] = stuff
> >   end
> > end
> >
> > If @foo_the_stuff is null, it will be initialized to an empty hash,
> > otherwise the existing value will be used. I consider this use of ||=
> > to be a Ruby idiom.
> >
> > Ryan
> >
> > On 5/22/06, Jeff Rose <rosejn@gmail.com> wrote:
> >> Have a module:
> >>
> >> Module Foo
> >>    def add_stuff(key, stuff)
> >>      @foo_the_stuff[key] = stuff
> >>    end
> >> end
> >>
> >> class Bar
> >>    include Foo
> >> end
> >>
> >> Is there a standard or correct way to initialize @foo_the_stuff in this
> >> example?  Should the add_stuff method check whether the variable has
> >> been initialized every time, or should this be done by implementing a
> >> callback like append_features or included?  (That's how I'd want to do
> >> it, but it's not clear which or how...)
> >>
> >> Thanks,
> >> Jeff
> >
> >
>
>
>