From: "David A. Black" <dblack@...>
Date: 2004-04-06T02:43:04+09:00
Subject: Re: deciding between ruby and python

Hi --

On Mon, 5 Apr 2004, Charles Comstock wrote:

> David A. Black wrote:
> 
> > for doesn't generate a result list though.  What you've got here will
> > return [3,2,1], and all the x+2 calculations will be discarded (like
> > #each).
>
> Hmm I had misunderstood that about each, I encountered it once, but 
> promptly forgot about it.  Do we do this to increase efficiency? 
> Otherwise I can't see a situation where you wouldn't want to return the 
> results of each for iteration.

There's definitely an efficiency issue; #each only has to keep the
current value in memory, whereas #map has to create a new array.  We
definitely want a way to iterate through things without creating a
result array in memory (think about going through the lines of a
multi-gigabyte file, for instance).  

Also, #map and #each tend to do different things.  For example:

  arr.each {|e| p "Current element: #{e}"}

If you map'd that, you'd end up with an array of nils (the return
value of #p), which would be pretty pointless.

So it's a mixture of efficiency ("low impact" iterating) and somewhat
different applications.


David

-- 
David A. Black
dblack@wobblini.net