From: Robert Klemme <shortcutter@...>
Date: 2007-12-07T22:28:17+09:00
Subject: Re: Dynamic local vars

2007/12/7, Vasyl Smirnov <vasyl.smirnov@gmail.com>:
> I wonder if there is any way to create local variables dynamically,
> for example, given
>
> def foo
>   bar
>   puts x, y
> end
>
> is it possible for bar to somehow create and initialize x and y?
> Binding doesn't seem to be modifiable..

You cannot do this easily because of the method / variable ambiguity.
There's a hack to do it: you need to define them before you use them
but it is ugly and does not work properly.

14:23:17 ~
$ ruby <<XXX
> def foo
> x=y=nil
> bar(binding)
> puts x,y
> end
> def bar(b)
> eval("x=1;y=2",b)
> end
> foo
> XXX
1
2

The problem with dynamically introducing local variables is that your
code needs to be statically aware of them in order to use them.  Even
though you can inject any number of additional local variables into a
binding, they won't get used because they do not appear in the code of
that method.

A much better solution to the problem of storing dynamic values is a Hash.

def foo
  data = {}
  bar data
  puts data[:x], data[:y]
end

def bar(x)
  x[:x] = 1
  x[:y] = 2
end

But you can as well return multiple values

def foo
  x,y = bar
  puts x, y
end

def bar
  return 1,2
end

Kind regards

robert

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