From: ara.t.howard@...
Date: 2006-03-29T07:53:47+09:00
Subject: Re: Opposite of ||= pattern?

On Wed, 29 Mar 2006, Justin Bailey wrote:

> A cheap just-in-time initialization trick is the "||=" trick:
>
> def add_name(n)
>  @name ||= Array.new
>  @name << n
> end
>
> Now, how would you do the opposite of this pattern? More specifically, what
> kind of construct would evaluate to a true value once, and then nil from
> then on? I came upon this in the context of for loops, where I want a
> one-time "starting" value to be present the first time through the loop,
> then nil. And I wanted to do it in a cool way  - i.e. not just assign the
> value to nil at the end of the loop, though of course that is the easiest
> way.
>
> Any thoughts?
>
> Justin

harp:~ > ruby -e' 3.times{ p( @x ? nil : @x=42) } '
42
nil
nil


regards.

-a
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