From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-06-13T16:56:13+09:00
Subject: Re: How to ducktype a Hash?

At 20:23 12/06/2004 +0900, you wrote:
>Sean O'Dell wrote:
>> So, how do I positively identify when an object is a hash or at least behaves 
>> like a hash?
>
>Use the method #to_hash instead. All hash-like objects should be able to
>give a hash-representation of themselves.
>
>        Rene

This makes a lot of sense to me. It seems to be symmetric
to to_str() too, which is good.

As a matter of fact, my rcr.rb has a to_hash() for Array:

  # Have Array.to_h() return an ArrayAsHash.
  # Please note that aa.to_h().to_a() == aa, which was the initial intend.
  class Array
    def to_h()
      h = ArrayAsHash.new()
      each_index do |ii| h[ii] = self[ii] end
      return h
    end
  end

  # What you get when converting an Array into a Hash, see Array##to_h()
  # It is a Hash with keys that are integer indexes (from 0 up to size of hash).
  class ArrayAsHash < Hash
    def to_a()
      super().sort_by { |(k,v)| k }.collect { |(k,v)| v }
      # ToDo: There must be a faster solution to do that.
    end
  end

  # Have Hash.to_a() return an HashAsArray instead of an Array.
  # Besides the class there are no other difference.
  class Hash
    alias ruby_to_a to_a unless defined? ruby_to_a
    # Returns an array of [key,value] pairs.
    # Please note that h.to_a().to_h() == h for most purposes.
    def to_a()
      HashAsArray.new().replace( ruby_to_a())
    end
    # Returns self. Much like Array##to_a() does.
    def to_h()
      self
    end
  end

Yours,

JeanHuguesRobert

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