From: "David A. Black" <dblack@...>
Date: 2010-08-08T08:12:00+09:00
Subject: Re: question about sub-class of array

Hi --

On Sun, 8 Aug 2010, warren ferguson wrote:

>
> I don't understand why thsi isn't working. I wanted to introduce a subclass of the Array class called Bitvector. A bit vector is an array of 0s and 1s, ordered from lsb at index 0 to msb at the highest index, so
> "10011" as a string would be [1,1,0,0,1] as an Bitvector. Here's what I tried:
>
> class Bitvector < Array
>  def initialize(*)
>    @a = super
>  end
>  def to_s
>    # convert Bitvector, ordered lsb to msb,
>    # to string of 0s and 1s, ordered msb to lsb
>    @a.map{|i| i.to_s(2)}.reverse.join
>  end
> end
> class String
>  def to_bv
>    # convert bit string of 0s and 1s, ordered msb to lsb,
>    # to Bitvector, ordered lsb to msb
>    Bitvector.new(self.reverse.split(//)).map{|k| k.to_i(2)}
>  end
> end
> # ----------------------------
> v = "10011".to_bv
> puts "v.class = #{v .class}"
> puts "v = #{v}"
> puts "--"
>
> v = Bitvector.new([0,1])
> puts "v.class = #{v .class}"
> puts "v = #{v}"
>
> The output from this program is
>
> v.class = Array
> v = [1, 1, 0, 0, 1]
> --
> v.class = Bitvector
> v = 10
>
> What I don't understand is why the first part reports v is of class Array, instead of class Bitvector.

It's because of the map operation, which returns an Array.


David

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

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