From: "David A. Black" <dblack@...>
Date: 2004-09-29T05:37:21+09:00
Subject: Re: DRY ruby idiom

Hi --

On Wed, 29 Sep 2004, stevetuckner wrote:

> I often use the ||= idiom in ruby for late initialization. But was 
> recently looking for an idiom that would allow me to overwrite a 
> variable if the right side is defined without repeating myself.
> 
> I have used the following:
> 
> var = val if val
> 
> but I have to repeat val and that violates DRY. 

  $ ruby -e 'a = b if b'
  -e:1: undefined local variable or method `b' for main:Object
  (NameError)


> I thought maybe &&= would work, but did not
> 
> var &&= val
> 
> That only works if var and val are non-nil. 
> 
> Any ideas out there?

I'm not sure it's possible, but it might depend on what state you want
to leave things in under what conditions.  Even if you do this:

  var = val if defined?(val)

var ends up being nil if val is *not* defined -- so that's
indistinguishable from the case where val exists and is nil.  If it's
OK for var to be nil, then that would be OK, otherwise not.  


David

-- 
David A. Black
dblack@wobblini.net