From: Robert Klemme <shortcutter@...>
Date: 2006-07-06T23:55:14+09:00
Subject: Re: attribute reader

ChrisH wrote:
> Just Another Victim of the Ambient Morality wrote:
>> "Robert Klemme" <shortcutter@googlemail.com> wrote in message
>> news:4h1o45F1p7ma2U1@individual.net...
>>> class Times
>>>   attr_accessor :time
>>>
>>>   def time_seconds
>>>     self.time.sec
>>>   end
>>>
>>>   def now
>>>     self.time = Time.now
>>>   end
>>> end
>>     As an aside, I'm still learning Ruby and am curious to know why you
>> choose to use self.time instead of @time.  Is there some sort of gatcha
>> about using instance variables (object variables?) that I don't know about?
>>     Thank you...
> 
> attr_accessor :time creates an attribute (@time) and two accessor
> methods:
>    def time
>    #return the value in our attribute
>      @time
>    end
> 
>    def time=(other)
>    #set the attribute to the given value
>      @time = other
>    end
> 
> 
> self.time.sec calls the time method of self to get the value of @time
> and calls the method sec on it
> 
> self.time = Time.now assigns the value of Time.now to the attribute via
> the time= method of self.
> cheers

That's how it technically works.  The *reason* I choose to do that is 
that the accessor method provides more abstraction.  If a sub class 
chooses to override this method all will still work as expected whereas 
directly using the instance variable is more likely to break.  Another 
thing to keep in mind is for example, if the implementation of 
attr_accessor changes and the value thusly is not stored in @time but 
somewhere else - self.time will then still work whereas direct access to 
the member will break.

And you have to use "self.time=" instead of "time=" because the latter 
will create a local variable of that name.

Kind regards

	robert