From: David Masover <ninja@...>
Date: 2008-08-21T11:11:17+09:00
Subject: Re: Can Someone Explain This to Me?

On Wednesday 20 August 2008 00:38:43 Ron Green wrote:
> class Body
>   @feet = 2
>   puts "We have #{@feet} feet"
>   def initialize
> 
>   end
>   def report
>     puts "We have #{@feet} feet"
>   end
> end
> 
> b=Body.new
> b.report
> 
> Why is it in the above class the first puts prints correctly but the second
> puts doesn't have a value for the instance variable?

Well, in this case, you're defining an instance variable... on Body, the 
class:

> class Body
>   @feet = 2

You see, classes are objects, too. You can treat them like normal objects:

b = Body
c = b.new

The normal way to do what I think you're wanting to do here is:

class Body
  def initialize
    @feet = 2
  end
end

By the way, you can leave out initialize if you have nothing to initialize.

Of course, if you're only supporting humans, you could do this:

class Body
  FEET = 2
  def report
    puts "We have #{FEET} feet"
  end
end

One more thing: I don't often use instance variables directly. That gives me 
more flexibility -- I can do something like this:

class Body
  attr_reader :feet
  def initialize
    @feet = 2
  end
  def report
    puts "We have #{feet} feet"
  end
end

That way, I could change to using a constant without touching the "report" 
method. The next version would look like this:

class Body
  FEET = 2
  def feet
    FEET
  end
  ...
end

But it's getting a bit silly talking about feet, so I'll stop.