From: dblack@...
Date: 2006-01-29T23:35:13+09:00
Subject: Re: Loop weirdness

Hi --

On Sun, 29 Jan 2006, Jonathan Leighton wrote:

> Okay, so let me get this right... if you do
>
> foo.each { }
>
> foo is re-evaluated with each iteration? Hence the bug? Why?

The length of foo is re-evaluated each time; that's how the decision
is made whether or not to keep iterating.  Array#each essentially
works like this:

   def each
     i = 0
     while i < length
       yield self[i]
       i += 1
     end
     self
   end

So if the length of the array increases in mid-stream, the iteration
will continue, based on the while test.

You can always get around this with something like:

   array.length.times do |i|
     # do something with array[i]
   end

where length won't be re-evaluated.


David

-- 
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming May 1, 2006!
http://www.manning.com/books/black