From: Shannon Fang <xrfang@...>
Date: 2005-10-25T12:10:18+09:00
Subject: RCR: Array#to_h

Hi there,

I have registered 2 accounts for RCRkive, but all failed... So I posted 
here.

Abstract

A simple method that construct a hash from an array. Just like Hash#to_a 
return an array from hash.

Problem

Consider this cenario: I programmed a multi-threaded web page downloader. 
One of its input is an array of urls to download. In the program, I wanted 
to use a hash like {'http://ruby-lang.org/index.html' => '200'}, i.e., use a 
hash to record the return code of the http request. This way I can avoid 
re-download a page, or miss a page.

For the user of this download program, it is much easier to use an Array 
instead of a Hash:

d = WebPageDownloader.new
d.links = IO.readlines('list.txt')

Hence, in the program we want to do:

@links = @links.to_h

Proposal

Add a method to_h (not to_hash) in the Array class, so that user can:

a = [1, 2, 3, 4, 5]
p a.to_h { |i, v| v * 2}  --> {5=>10, 1=>2, 2=>4, 3=>6, 4=>8}
p a.to_h(3)                 --> {5=>3, 1=>3, 2=>3, 3=>3, 4=>3}


Anaysis

This is very convenient for users who need this feature, and it will not 
affect behavior of the Array class in anyway for those do not need this 
feature.

Please refer to RCR278, which is similar but not same.

Implementation

class Array
  public
  def to_h(value = nil)
    _hash = {}
    self.each_index do |i|
      v = self[i]
      if block_given? then
        _hash[v] = yield(i, v)
      else
        _hash[v] = value
      end
    end
    _hash
  end
end

Please comment.

Thanks,
Shannon