Creating variable with eval

ruby-talk
1

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.

···

-----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

2

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