From: Dave Thomas <dave@...>
Date: 2004-11-12T10:53:33+09:00
Subject: Re: ruby idiom for attribute definition?


On Nov 11, 2004, at 19:43, Yukihiro Matsumoto wrote:

> Hi,
>
> In message "Re: ruby idiom for attribute definition?"
>     on Fri, 12 Nov 2004 04:06:39 +0900, Dave Thomas 
> <dave@pragprog.com> writes:
>
> |That's why I said you have to use the accessor methods. Structs cheat.
>
> I don't consider it cheating.  Accessing instance variables is sort of
> cheating (that's part of the reason for ugly "@").

Except in structs you still have the instance variables (the state has 
to be somewhere). You just can't access them. That's what I meant by 
cheating... :)

> |Matz: we discussed this before, but it would be really nice if Struct
> |set up the IVs too: that way this idiom would be more generally 
> useful.
>
> Hmm, instance variables are internal information. If you don't know
> the internal, you should use accessors (self.a this case), even in the
> methods.  I'm not excited for Structs to have their members in
> instance variables.

Agreed in general (in fact I argued that a couple of posts back). But 
the idiom

    class A < Struct(:x,  :y)
    end

could be really useful for classes that want IVs initialized from the 
constructor, and which provide accessors for them by default, that I 
wonder if we could bend the rules :)  I tend to use the construct for 
Structs where I want to add just one or two helper methods.


Cheers

Dave