From: Gavin Sinclair <gsinclair@...>
Date: 2002-11-04T08:32:02+09:00
Subject: Re: Extending Hash

From: "Carl Youngblood" <carl@youngbloods.org>

> I'm trying to create a modified version of a Hash that, if it doesn't contain
anything for a given key, will return whatever element it has that most closely
matches the key.  Here's what I've done so far:
>
> -----------------------------------
> class FragHash < Hash
>         def [](key)
>                 index = key.dup
>                 while !self.has_key?(index) and index.chop! != nil
>                 end
>                 return self.default if index.empty?
>                 return fetch(index)
>         end
> end
> -----------------------------------

A Ruby-idiomatic way to do the while loop might be:
  1 until self.has_key?(index) or index.chop! == nil

Use it if you think it's more readable.

> so if I do the following:
>
> -----------------------------------
> h = FragHash.new
> h['t'] = 23
> puts h['test']
> -----------------------------------
>
the output is 23.  In other words, it didn't find the index "test" but it kept
shortening the index until it found something that matches.  The only problem I
have now is that I want to make it so that when I call each() it also
enumerates through the default value.  However, I don't know how to extend the
each function (I'm still a little hazy on how to overload functions that use
blocks).  It would be nice if I could look at the source for the Hash class
itself.  Does anyone know where I can find it?  Does anyone have any
suggestions for how I might modify the each function?
>
> Thanks,
> Carl Youngblood


I'm not actually sure or your problem here Carl.  What do you mean by the
"default" value?  In your example above, won't "each" yield ["t", 23]?

Anyway, overriding each is not too hard.  Here's how you could implement
Hash#each from scratch if you wanted to.  You can hopefully use this to
implement the functionality you want.  (Warning, not tested.)

class Hash
  def each(&block)
    self.keys.each do |key|
      value = self.[key]
      block.call(key, value)
    end
  end
end


Hope this helps,
Gavin