From: "David A. Black" <dblack@...>
Date: 2010-08-08T09:05:01+09:00
Subject: Re: question about sub-class of array

Hi --

On Sun, 8 Aug 2010, Warren Ferguson wrote:

> I'm stil mystified why substituting the expression for v into
> Bitvector.new(v) fails. Is it because Ruby optimizes that complex
> expression by realizing the expression is of class Array and Bitvector
> is a subclass of array?

No; it's because you weren't doing what you think you were doing :-)

Here are the two versions:

     Bitvector.new(self.reverse.split(//)).map{|k| k.to_i(2)}

     v = self.reverse.split(//).map{|k| k.to_i(2)}
     Bitvector.new(v)

In the first one, you're calling map on a Bitvector object. In essence
it's this:

     bv = Bitvector.new(self.reverse.split(//))
     return bv.map{|k| k.to_i(2)}

In the second one, you're doing the map operation first, and then
sending the result of that operation to the BV initializer.

Move the parentheses around in the first one and you'll see what I mean:

     Bitvector.new(self.reverse.split(//).map{|k| k.to_i(2)})


David

-- 
David A. Black, Senior Developer, Cyrus Innovation Inc.

   The                   Ruby training with Black/Brown/McAnally
   Compleat              Philadelphia, PA, October 1-2, 2010
   Rubyist               http://www.compleatrubyist.com