From: Raul Jara <raul.c.jara@...>
Date: 2010-02-28T07:32:11+09:00
Subject: Re: scope question

Nick Brown wrote:
> Consider the following Sinatra app:
> 
> require 'sinatra'
> vara = "foo"
> VARB = "bar"
> helpers do
>   def geta
>     vara
>   end
>   def getb
>     VARB
>   end
> end
> get '/a' do geta end
> get '/b' do getb end
> 
> When I run that and browse to /b, it displays "bar". When I browse to
> /a, however, it produces the error: "undefined local variable or method
> `vara'".
> 
> Why do these two variables differ in scope?
> 
> How can I declare a variable that has global scope but is not a
> constant?
> 
> Thanks in advance...

Important disclaimer: I'm kind of new at this, so I'm just taking a stab 
at it...

One way you could do that is to declare a class variable for the class 
Object.  Because every object inherits from Object, everything in ruby 
should have access to that same class variable.  E.g.,

class Object
  @@var = "Hello"
end

puts @@var
>Hello

class Silly
  def Silly.hi
    puts @@var
  end
end

Silly.hi
>Hello

@@var = "goodbye"

Silly.hi
>goodbye



But it's generally considered good form to not use global variables in 
the first place.  There's almost always a way to avoid using them. The 
danger of using them is that if you use a global variable with your 
code, and someone else uses a global variable of the same name in their 
code, the two bits of code will both break if they are ever run 
together.
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