From: Stefan Kaes <skaes@...>
Date: 2005-05-30T22:40:42+09:00
Subject: Re: creating variable with eval

Robert Klemme wrote:

>This comes up again and again.  You might want to search the archives.
>  
>
This comes up again and again because the current behaviour is 
inconsistent with the proudly stated principle of least suprise. As I 
have said before: eval "code" should be equivalent to code in all contexts.

>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
>
>  
>
However,

$ irb
irb(main):001:0> eval "x=10"; p x
NameError: undefined local variable or method `x' for main:Object
        from (irb):1
irb(main):002:0> eval "x=10"
=> 10
irb(main):003:0> p x
10
=> nil
irb(main):004:0> exit

If this isn't bound to be confusing ...

Regards,

Stefan