From: Joel VanderWerf <vjoel@...>
Date: 2005-12-19T06:27:40+09:00
Subject: Re: Newbie: require 'filename'  - undefined local variable or method...

Grehom wrote:
> I have one line of code in a file called 'stuff.rb':
>      myhash = { "a" => "ay", "b" => "bee", "c" => "sea" }
> 
> and I wish to include it in another program called 'mainprog.rb' thus:
> 
>      require 'stuff'
> 
>      puts " a = " + myhash["a"]
> 
> when I run it I get an error message:
>     mainprog.rb:4: undefined local variable or method `myhash' for
> main:Object (NameError)

Local vars are scoped to the file they are defined in, when you use
require or load. You could make it global, but unless this is just a
quick hack, it's not a good solution.

Another option is to read and eval the file. If the myhash variable has
been assigned *before* you eval, then the assignment in stuff.rb will
propagate to the mainprog.rb. Like so:

  myhash = nil
  eval File.read("stuff.rb")
  p myhash

This is ok for some purposes, but you have to know in advance which
variables the file is going to define. Also, you may have scope
collisions: any other local var in mainprog.rb can be affected by
assignments in stuff.rb.

My preference is to read the file as a string and use module_eval:

# mainprog.rb
  m = Module.new
  m.module_eval(File.read("stuff.rb"), File.expand_path("stuff.rb"))
  p m::Myhash

# stuff.rb
  Myhash = { "a" => "ay", "b" => "bee", "c" => "sea" }

Local vars stay local. Constants are accessible in the scope of the
newly defined module m. The second arg to module_eval means that errors
are reported with the correct file name.

<plug> This is the approach used by my "script" lib on raa. It adds some
sugar and features. </plug>

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407