From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2008-02-26T20:10:50+09:00
Subject: Re: attr_writer vs attr_accessor

On Tue, Feb 26, 2008 at 11:09 AM, ycsunil <ycsunil@gmail.com> wrote:
> On Feb 26, 2:38 pm, Thomas Wieczorek <wieczo...@googlemail.com> wrote:
> > On Tue, Feb 26, 2008 at 9:29 AM, ycsunil <ycsu...@gmail.com> wrote:
>  > > Hello all,
>  >
>  > >  From readings I understood that attr_accessor is the one which has the
>  > >  property of attr_reader and attr_writer. If we define a variable as
>  > >  attr_writer, we can use it to read and write as well. My question is;
>  > >  why do we need to use attr_accessor since attr_writer does the job of
>  > >  read and write?
>  >
>  > Did you try it? I get an error, when I use the following
>  >
>  > irb(main):001:0> class Foo
>  > irb(main):002:1> attr_writer :bar
>  > irb(main):003:1> def initialize
>  > irb(main):004:2> @bar = "hallo"
>  > irb(main):005:2> end
>  > irb(main):006:1> end
>  > => nil
>  > irb(main):007:0> Foo.new.bar
>  > NoMethodError: undefined method `bar' for #<Foo:0x2ad5640 @bar="hallo">
>  >         from (irb):7
>  > irb(main):008:0>
>  >
>  > attr_writer just creates the bar=(value) method, no bar() method to
>  > access the attribute.
>
>  Thanks! for clearing the doubt with an example. In general I thought;
>  if varialbe can be writable then it should hold property of
>  readable... which is not true in attr_writer.

attr_xxx do not "declare" any property or type of property.
They just generate methods.
attr_reader :xxx generates a method that returns the value of the
instance variable @xxx
attr_writer :xxx generates a method xxx= that sets the value of the
instance variable @xxx
attr_accessor :xxx generates the two above methods.

Hope this helps,

Jesus.