From: Robert Klemme <shortcutter@...>
Date: 2008-01-18T21:37:29+09:00
Subject: Re: Create variables with caller scope

2008/1/18, Jari Williamsson <jari.williamsson@mailbox.swipnet.se>:
> Jean-François Trân wrote:
> > Jari Williamsson :
> >> Is it possible for a method to create new variables that
> >> becomes in the scope of the caller (instead of the scope
> >> of the method)? I guess I mean to get a method to behave
> >> much like macros or templates in C/C++.
> >
> > Why not using a block ?
>
> Because the created variables will "only" get block scope, if I
> understand your sample code correctly. And calling the
> create_some_variables() multiple times would create multiple stacked blocks.
>
> But giving it a bit more thought, I think I should redesign the code a
> bit and let the method instead dynamically create a class where all the
> created variables are stored and then returned an instance of that class.

OpenStruct and Hash come to mind.  One of those is usually far better
than the hack you attempted initially.  Btw, there is another issue
with this: local variables created dynamically in a scope cannot be
used directly (i.e. the same way as if they were defined in the scope
directly):

$ ruby -e 'def f() eval("x=1", binding); p x end; f'
-e:1:in `f': undefined local variable or method `x' for main:Object (NameError)
        from -e:1
13:35:55 /cygdrive/c/SCMws/RKlemme/OPSC_Gold_bas_dev_R1.2_perf/bas
$ ruby -e 'def f() eval("x=1", binding); p(eval("x", binding)) end; f'
1
13:36:27 /cygdrive/c/SCMws/RKlemme/OPSC_Gold_bas_dev_R1.2_perf/bas

So you need to use some name passing mechanism anyway.  And if you do
that you can use a Hash immediately which is much easier and clearer.

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end