From: Brian Candler <B.Candler@...>
Date: 2004-09-19T01:23:52+09:00
Subject: Re: Accessing Hash elements in sorted order?

On Sat, Sep 18, 2004 at 04:58:13AM +0900, Markus wrote:
> > > There has been some discussion going on whether Ruby's Hash should be 
> > > sorted by default on this list recently.
> > > 
> > 
> > I would vote in favor of it.
> 
>      I'd vote against, for the following reasons.
> 
>      1. Every time it comes up the thread goes quite a while before the
>         advocates realize that they aren't all assuming the same sorting
>         order.  Some are thinking "sorted by key (obviously)" while
>         others are thinking "sorted by order of insertion (obviously)"
>         and still others are thinking "sorted by value" or "sorted by
>         some arbitrary key so long as it's consistent," etc.
>      2. Many of the proposals are not particularly well defined when you
>         consider issues like modification and alternate means of
>         construction.
>      3. Hash, like String, Array, etc. is a fairly well established data
>         structure.  Although it might for some uses be nice to have a
>         string where the characters were "automatically" sorted into
>         alphabetical order, this isn't what anyone familiar with strings
>         would expect. 
>      4. It may well impose a significant performance penalty
>      5. It may well break existing code
>      6. It is easy enough to produce the desired effect(s) by other
>         means.

7. It would almost certainly no longer be a Hash!! In other words, to get
any efficiency for the 'each' method, you would have to implement it as a
B-Tree or similar data structure, not a hash. I'm sure there's a tree
library in RAA, so you can always just use that instead.

That's unless 'sorted' simply means 'kept in order of insertion'. In that
case, it could be a combination of a hash and a doubly-linked list. But that
means it still wouldn't be just a hash.

Regards,

Brian.