From: Gavin Kistner <gavin@...>
Date: 2005-08-25T23:56:03+09:00
Subject: Re: determining the attribute names of an object

On Aug 25, 2005, at 8:45 AM, David A. Black wrote:
>> Some people (read: me) have incorrectly assumed that Struct is
>> "shorthand squared" for defining a class, an initialize, and
>> a bunch of accessors. But the behavior is different.
>
> I'm just not sure where you would experience a need for that.  What
> would that enable you to do that you can't do now?  I'm thinking you
> could always use self.member = x instead of @member = x, in other
> methods, which is arguably a good idea anyway.

I think you're correct; I think the problem is simply one of  
consistency.

I expected #puts and #print to output their code inline in an ERB  
template, but (until I hacked the source) they didn't. There were at  
least two other ways to achieve the same effect, but it causes a  
context switch when I'm merrily coding along and have to say "Oh,  
shit, I forgot, I'm inside __this__ case...I need to write my code a  
little differently."

I feel the same way with Struct...it would be convenient to be able  
to write:

Person = Struct.new( :first, :last )
class Person
     def fullname
         "#@first #@last"
     end
end

because that's what I (and many others) expected the implementation  
detail of Struct-created classes to be. Certainly, it's just as easy  
to write:

Person = Struct.new( :first, :last )
class Person
     def fullname
         "#{first} #{last}"
     end
end

And as you say, it is arguably a good idea to use internal methods of  
the class to minimize coupling between methods. (Am I correct in  
assuming that this may result in a non-trivial performance hit,  
however, invoking methods versus using instance-variable lookup?)  
It's just a 'special case' from what appears to be the mental model  
of many people.