From: Nat Pryce <nat.pryce@...13media.com>
Date: 2002-11-01T01:42:37+09:00
Subject: Re: method-call style (was Re: Snippet: Tiny Featureless Ruby Web	Server)

On Thu, 2002-10-31 at 16:04, Albert Wagner wrote:
> On Wednesday 30 October 2002 12:13 pm, Nat Pryce wrote:
> > On Wed, 2002-10-30 at 17:38, William Djaja Tjokroaminata wrote:
> > > dblack@candle.superlink.net wrote:
> > > > I don't think one should make that assumption; it's awfully rigid.  I
> > > > might have:
> > > >
> > > >   def stuff=(x)
> > > >     @thing = x
> > > >   end
> > > >
> > > >   def stuff
> > > >     @thing
> > > >   end
> > > >
> > > > which is a dinky example at best... but meaning there is no necessary
> > > > connection between the methods and the implementation.
> > >
> > > Well, it looks like a contrieved example, so it is really a matter of
> > > personal style/convention.  But now suppose that someone really writes a
> > > code like above in a class, and I want to derive a new class from it, and
> > > I need to access "the object logically represented by
> > > stuff/thing".  In my derived class, should I use "@thing" or should I use
> > > "self.stuff"?
> >
> > Definitely use self.stuff to avoid breaking encapsulation.
> >
> > Imagine if the class was instead:
> >
> >   def stuff=(x)
> >      @thing = x + 1
> >   end
> >
> >   def stuff
> >      @thing - 1
> >   end
> >
> >
> > Using @thing as a synonym for self.stuff would give the wrong result.
> 
> Of course they give different results: @thing is a state variable, stuff= 
> modifies the state variable, and stuff is simply an algorithm that happens to 
> utilize the state variable.  Assuming that stuff and @thing are synonymous is 
> what is wrong.

Exactly my point!  And it looks like a trivial point when illustrated
with the code above.  However, the point is as valid, although much less
obvious to many programmers, when illustrated with David Black's
original code, which was a direct assignment to and return from an
instance variable.  And the point is even less obvious when the accessor
functions have the same name as the instance variable:

    def stuff
        @stuff
    end

    def stuff=( new_stuff )
        @stuff = new_stuff
    end

Cheers,
	Nat.

-- 
Dr. Nathaniel Pryce, Technical Director, B13media Ltd.
Studio 3a, 22-24 Highbury Grove, London N5 2EA, UK
http://www.b13media.com