From: Philip Hallstrom <ruby@...>
Date: 2006-05-11T18:26:09+09:00
Subject: Re: Writable attributes - how does this work?

> How does this actually work?
>
> from the Pick Axe book:
>
> irb>
> 1>  class Song
> 2 >  def duration=(new_duration)
> 3>     @duration = new_duration
> 4>   end
> 5> end
> 6>
> 7> song = Song.new("Bicylops", "Fleck", 260)
> 8> song.duration --> 260
> 9> song.duration = 257
> 10> song.duration --> 257
>
> If a method name which is used to set the attribute is called
> "duration=", how come that one can use song.duration = 257?
>
> I mean, does it just work lik this, because the Ruby engine recognizes
> the 'set attribute' method just because of the = sign after the
> "duration" on line number two?

You'll probably get better answers from someone who is smarter than I am, 
but since it's late and I'm waiting for something to finish, here's how I 
think about it...

Stop thinking of =, ==, +, *, <=,.... as operators.  Think of them as 
methods.

So, when you see "a = b" that's really saying call the method "=" on the 
object "a" passing as an argument "b".  If you think of it that way then 
when you see the below method it will make more sense.

def a= (b)
   @a = b
end

So, "a + b" is really:

def a+ (b)
   return a + b
end

(yes, I know the return is unecessary, just trying to be clear :)

Hope that helps.