From: eliben@...
Date: 2006-03-12T02:23:43+09:00
Subject: Re: attribute setters for instance variables


Hans Fugal wrote:
> eliben@gmail.com wrote:
> > Hello,
> >
> > The Pickaxe book presents the following example:
> >
> > class Incorrect
> >   attr_accessor :one, :two
> >   def initialize
> >     one = 1
> >     self.two = 2
> >   end
> > end
> >
> > obj = Incorrect.new
> >
> > p obj.one
> > p obj.two
> >
> > The first thing printed is 'nil' and not '1' since "one = 1" assigns to
> > a local variable of method initialize instead of the instance variable.
> > So far it's clear.
> > Now, they propose a solution: to use self.one instead of just one.
> > Won't be using @one simpler and also correct ? What am I missing ?
> >
> > Thanks
> >
>
> @one = 1 is setting the instance variable itself, and that's fine for
> accessors. If you want to do something special on =() then you will want
> to use the self.one style. e.g.
>
> def Foo
>    def one=(n)
>      @one = n+42
>    end
>    def initialize(n)
>      self.one = 0 # @one == 42
>      @one = 0     # @one == 0
>    end
> end

Thanks for your swift and insightful reply.