From: Joe Van Dyk <joe.vandyk@...>
Date: 2004-11-13T05:13:27+09:00
Subject: Re: automatically call function on attribute set


"Joel VanderWerf" <vjoel@PATH.Berkeley.EDU> wrote in message
news:4193C096.7070007@path.berkeley.edu...
> Joe Van Dyk wrote:
> > Joel VanderWerf wrote:
> >
> >>     def fly
> >>       self.x += 1   # don't use @x=, or else no
> >>     notification end
> >>   end
> >>
> >
> >
> > What is the difference between self.x and @x?
>
> In ruby, assigning to an instance variable @x like
>
>    @x += 1
>
> does not invoke any methods (except the + method of the Integer class,
> in this case). So there's no way for the Airplane class to detect the
> assignment and (in this case) notify observers.
>
> By contrast, the code
>
>    self.x += 1
>
> forces a call to the method "x=", which has been defined by "observable
> :x" to both set the value of @x and to notify observers.
>
> And just for completeness, the code
>
>    x += 1
>
> can only assign to a local variable, even if "x=" has been defined as a
> method.
>
>

Ok.  In general, it's best to use self.x as opposed to @x?