From: Fergal J Byrne <editor@...>
Date: 2006-08-22T03:54:39+09:00
Subject: Re: A use case for an ordered hash

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Rick DeNatale wrote:
> On 8/21/06, Bil Kleb <Bil.Kleb@nasa.gov> wrote:
>> Phillip Hutchings wrote:
>> > Using an ordered hash for one
>> > person's benefit would kill the speed and jack up memory usage.
>> >
>> > [..] but replacing the Hash is not the way to go.
>>
>> I don't think anyone is suggesting replacing the
>> existing Hash.  As I see it, the ordered hash would
>> merely be an alternative to the standard hash.
> 
> Which, as has been shown can be provided without changes to the base
> specification/implementation of Ruby.
> 
> The fly in the ointment, is that a few of the proponents of
> OrderedHash seem to strongly require a literal syntax for the beast.
> That's the one thing which seems to require divine intervention <G>.

This functionality is not part of Hash as traditionally
understood, including those new to Ruby. Adding it to the
core Hash in the language will add a space and time cost
to all programs currently using Hash.

If you need a hash with this functionality, create a
mixin module containing the extra code (several examples
have appeared in these threads) and include it where
you need it.

I often have a hankering for this kind of functionality
in random access data structures (database tables more
than in-memory structures), so I can see the use of it.

Doesn't strike me as a must-have addition (or subtraction)
for the core Hash class...

And I wouldn't call it an OrderedHash (suggests sorting
by the data rather than by insertion order). Call the
mixin something like InsertionOrderMemory and you could
conceivably use it for other structures...

- --

regards

fergal byrne
technical director

Adnet Web Development - Building for Business since 1995
http://www.adnet.ie/  t:+353 1 676 4262 aim/skype:FergByrne

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