From: Karsten Meier <discussionruby@...>
Date: 2004-03-31T07:24:23+09:00
Subject: Re: [newbie] linked hash


Making a subclass of a standard class like Hash can be dangerous,
you should verify that it works for all methods, otherwise you may get 
surprises:

h = OrderedHash.new
h['key1'] = 1
h['key2'] = 2
h.delete('key1')
Now 'key1' is still in the '@ordered_keys' array, and methods like 
'keys' and 'each' will  give you wrong results.

Regards

Karsten Meier


> 
> no ordered only as it is entered, in the mean time i've found a solution
> :
> 
> # OrderedHash.rb
> 
> class OrderedHash < Hash
> 
> VERSION = "2004-03-28"
> 
>         def []=( key, value )
>                 ( @ordered_keys ||= [] ) << key unless has_key?( key )
>                 super
>         end
> 
>         def each
>                 @ordered_keys.each do | key |
>                 yield key, fetch( key )
>                 end if @ordered_keys
>         end
> 
>         def keys
>                 a = Array.new
>                 @ordered_keys.each do | key |
>                 a << key
>                 end if @ordered_keys
>                 return a
>         end
> 
>         def join_keys(s)
>                 return self.keys.join(s)
>         end
> 
>         def values
>                 a = Array.new
>                 @ordered_keys.each do | key |
>                 a << fetch(key)
>                 end if @ordered_keys
>                 return a
>         end
> 
>         def join_values(s)
>                 return self.values.join(s)
>         end
> 
> end
>