From: Jonathan Wills <runningwild@...>
Date: 2009-02-07T03:52:51+09:00
Subject: eval statement

Trying to switch a project of mine from python to ruby.  Love ruby so
far, but I'm finding that the eval statement is a bit more difficult to
use than python's exec statement.  Here is one of the problems I'm
having, RUBY_VERSION=1.9.1

a = 1
eval('a=2')
puts a

This will print out '2', as I want.  However if I remove the first line,

eval('a=2')
puts a

r.rb:2:in `<main>': undefined local variable or method `a' for
main:Object (NameError)


Now if in the first case eval can change a variable in its scope, why
can't it also create a variable in that same scope?  I may also not be
totally clear on the way ruby handles scoping, which might be part of
what I am having trouble understanding.

Any help understanding the eval statement would be appreciated.  I will
probably have more questions about it, but I'll leave at this for now.

thanks,
-Jonathan
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