From: dblack@...
Date: 2006-11-15T22:08:17+09:00
Subject: Re: Design problem with 'inject'

On Wed, 15 Nov 2006, Gary Boone wrote:

>
> Those are several good suggestions.
>
>   next sum if (i == 3)
>
> strikes me as simple and clear. Provided you know that the block result
> is what matters, you can stay out of trouble.

I think you're well advised to know that if you're using inject :-)

> Simplifying the example, the trouble with inject is that
>
>   arr.inject(0) { |sum, i| sum += i }
>   arr.inject(0) { |sum, i| sum + i }
>
> both produce the same result. Yuk.
>
> Maybe it should be posted somewhere as a potential 'gotcha'.

It's not, though; it's just how Ruby works.  When you do:

   sum += i

the parser turns it into:

   sum = sum + i

So you're just reusing the identifier 'sum'.  As with all
reassignment, the variable is completely reinitialized.


David

-- 
                   David A. Black | dblack@rubypal.com
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org