From: Florian Gilcher <flo@...>
Date: 2010-06-02T01:24:18+09:00
Subject: Re: using "require" in irb, where did my variables go!?


On Jun 1, 2010, at 4:23 AM, Tim Apple wrote:

> Hello,
> 
> I have a somewhat basic question: lets say that in my working directory
> I have a file called my_vars.rb.
> 
> It contains:
>  x = 5.0
>  puts "your variable x is #{x}"
> 
> Now, I fire up irb in my command window, and type in
>  require "my_vars.rb"
> 
> Which outputs, as expected,
>  your variable x is 5.0
>  => true
> 
> Now, I want to access that variable again, so I enter in:
>  puts x
> 
> and I get an error saying that x is undefined.  It's like it was
> temporarily there in memory, but then once it was used, it got thrown
> away!  Does anyone know how to load in a file and keep using the
> variables that were in said file?
> 
> Thanks!

There is a way around this, although I think that the "usual" solutions (wrapping this data into a proper object or method) are much better.

All code in Ruby is evaluated inside the context of an object. In other terms: self is always defined. Code outside of class statements, module statements and some special statements that change the binding is evaluated inside the toplevel object (called "main"). "main" is just a normal object and we can thus set instance variables:

  File: test.rb
    @b = 42
  
  File: inc.rb
    require "test"
    puts @b #=> prints 42

Those instance variables can only be accessed in the toplevel context and not in any other object or class.

I don't think this is a good way to do it, but it is a nice way of illustrating how far "everything is an object" is rooted into ruby.

Gruß,
Skade