From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2011-02-02T03:27:40+09:00
Subject: Re: attr_reader - general question

On Tue, Feb 1, 2011 at 7:11 PM, Jim Carter <jcarter@leupold.com> wrote:
> I have the following configuration:
>
> class ExternalBallistics
>
>    attr_accessor    :a,:b   #inputs
>    attr_reader      :c      #outputs
>
>    def initialize(&block)
>     instance_eval &block
>    end
>
>    def calculate
>       c = a + b

This is not calling the method "c=", not that you have one, in any
case. "c" is considered a local variable.
Change it to:

@c = a + b

to set the value in the instance variable that your reader will access.

>    end
>
> end #class
>
>
>
> ExternalBallistics.new do
>
>   self.a = 5
>   self.b = 3
>
>   calculate
>
>   puts self.c
>
> end #ExternalBallistics
>
>
> This returns a nil value for c.  If I use "puts" inside of def
> calculate, I will get 8 for an answer.  Why does a and b act globally
> and c not.  Am I forced to use a return on calculate to get an answer.
> If I do so, do I still need to define an attr_reader :c (what use is it
> then) ?
>
>
> Thanks

Jesus.