From: "David A. Black" <dblack@...>
Date: 2009-02-16T00:22:30+09:00
Subject: Re: Iterating a changing Hash under 1.9.1

Hi --

On Sun, 15 Feb 2009, Phrogz wrote:

> The following code shows that Hash#each under 1.9.1p0 does not iterate
> over keys added during iteration:
>  a = [ 1, 2, 3 ]; h = { 0=>0 }
>  h.each{ |k,v| h[a[k]] = a[k] }
>  p h
>  #=> {0=>0, 1=>1}
>
> However, this code (on 1.9.1p0) results in a ruby process with
> unending 100% CPU usage, presumably due to an unending loop that keeps
> traversing newly-added items:
>  h = { 1=>nil, 2=>nil }
>  h.each{ |k,v| h.delete(k); h[k]=v }
> (Credit to "tama" for posting this on the ramaze group.)
>
> I'm assuming that one of these two are a bug, since they seem
> contradictory. I'd like to think that the latter behavior is the bug,
> and that hashes aren't supposed to iterate over keys added or moved
> during iteration. Can anyone confirm or deny this?

I can only add what I think is another interesting example:

h = {1,2,3,4}

h.select {|k,v|
   h[rand] = 1
   v > 4
}

This exits in 1.8 but goes on forever in 1.9. I'm not sure whether
it's because of the override that Hash#select does of
Enumerable#select.


David

-- 
David A. Black / Ruby Power and Light, LLC
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