From: google@... (Tom Payne)
Date: 2003-01-20T22:13:44+09:00
Subject: Re: Feature request: Array.to_h

dblack@candle.superlink.net wrote in message news:<Pine.LNX.4.44.0301181254230.23130-100000@candle.superlink.net>...
> Almost :-)  See <http://www.ruby-talk.org/6663>.  I seem to evade
> naming any of the variants just "to_h" (they're to_h_raw, to_h_ikeys),
> etc.  I'm inclined to think "to_h" would be what I called "to_h_raw",
> i.e.:  [1,2,3,4].to_h => { 1 => 2, 3 => 4 }, but I'm not sure.

I think of Arrays as mapping integers >= 0 to values, and of Hashes of
mapping arbitrary keys to values. So, for me, the POLS for Array.to_h
would be to produce a Hash that maps the same keys as the array to the
same values, i.e [:a, :b].to_h => {0 => :a, 1 => b}.

Your to_h ([1,2,3,4].to_h => { 1 => 2, 3 => 4 }) might be more
familiar to a PERL programmer. IIRC, in PERL hashes can be written
[key0, value0, key1, value1, ...], but I might be wrong.

N.B. Your implementation of to_h_raw from
<http://www.ruby-talk.org/6663>:

module Enumerable
  # The simplest to_h: array elements are taken two at a time.
  # (Not even indices -- just elements.)
  def to_h_raw
    a = dup
    h = {}
    h[a.shift] = a.shift || nil until a.empty?
    h
  end
end

should really be in the Array class, not the Enumerable module,
because it uses the shift method: Arrays have this, but Enumerables
don't.

An implementation using each (provided by Enumerable):

module Enumerable
  def to_h_raw(default = nil)
    result = Hash.new(default)
    key = nil
    index = 0
    each do |element|
      case index % 2
      when 0 then key = element
      when 1 then result[key] = element
      end
      index += 1
    end
    result[key] = nil if index % 2 == 1
    result
  end
end

[1, 2, 3, 4].to_h_raw => {1=>2, 3=>4}
[1, 2, 3, 4, 5].to_h_raw => {5=>nil, 1=>2, 3=>4}

Regards,

Tom