From: Robert Klemme <shortcutter@...>
Date: 2010-11-19T01:50:36+09:00
Subject: Re: Question on scoping

On Thu, Nov 18, 2010 at 4:21 PM, James Byrne <byrnejb@harte-lyne.ca> wrote:
> I clearly have either forgotten something important, or I never
> understood it correctly, but I cannot sort out what is wrong with the
> following:

You have fallen in the method local variable ambiguity trap.

> module AO_Map
>  .  .  .
>  def ao_map_module_method( y )
>   puts( current_batch.to_yaml )
> .  .  .
> end
>
> class Main
> .  .  .
>    require  file_dir + "/ao_map"
>    include AO_Map
> .  .  .
>    attr_accessor( :current_batch )
> .  .  .
>    def execute
>  .  .  .
>    current_batch = other_class_main_method( x ) # is a hash

   self.current_batch = other_class_main_method( x ) # is a hash

>    .  .  .
>    if current_batch
>    begin
>      .  .  .
>      ao_map_module_method( y )
>      .  .  .
> end
>
> This construct fails in ao_map_module_method with current_batch being
> nil.  Why?  What is it that I am not comprehending about variable scope
> in attempting to do this?

A call to an attribute setter (x=something) must always be prefixed
with a variable and a dot.  Otherwise the name is recognized to mean a
local variable and you do not see the getter any more.

> I know that I can pass current_batch in as a method parameter to
> ao_map_module_method but what is wrong with simply calling an accessor
> method from inside another method?  Presumably current_batch and
> ao_map_module_method are at the same level inside of class Main.

You're not actually calling the accessor but rather defining a local variable.

Kind regards

robert


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