comp.lang.ruby

Robert Klemme

5/30/2005 3:02:00 PM

Geert Fannes wrote:
> And is there any other way to create variables in a dynamical manner,
> using something else than eval(), or can only the parser create
> variables?
> Greetings,
> Geert.

You do in fact create them as one of my examples showed:

> 14:44:40 [source]: ruby -e 'eval("x=10");p(eval("x"))'
> 10

.... but they cannot be accessed from code that was compiled prior to
calling eval.

robert

>
> -----Original Message-----
> From: Robert Klemme [mailto:bob.news@gmx.net]
> Sent: 30 May 2005 14:55
> To: ruby-talk ML
> Subject: Re: creating variable with eval
>
>
> This comes up again and again. You might want to search the archives.
>
> Short story: Ruby determines local variables at parse time. Although
> you
> can bind values to local vars with eval you cannot access them outside
> of
> eval because they are not known there:
>
> 14:44:40 [source]: ruby -e 'eval("x=10");p(eval("x"))'
> 10
> 14:44:46 [source]: ruby -e 'eval("x=10");p x'
> -e:1: undefined local variable or method `x' for main:Object
> (NameError) 14:44:51 [source]: ruby -e 'x=nil;p x;eval("x=10");p x'
> nil
> 10
>
> Apart from that: your dynamic created variables will be of no use as
> the method body cannot access them. The simplest solutions:
>
> 1) Access the hash instead of using local vars
>
> 2) Generate the complete method code
>
> In any case: make sure you have default values so you can init
> variables not defined in the hash. Otherwise you'll see the same
> error:
>
> 14:48:05 [source]: ruby -e 'def x(a) b + a end;x 10'
> -e:1:in `x': undefined local variable or method `b' for main:Object
> (NameError)
> from -e:1
>
> Kind regards
>
> robert