From: Kristof Bastiaensen <kristof@...>
Date: 2004-09-04T17:00:21+09:00
Subject: Re: Hashes and ordering

On Sat, 04 Sep 2004 12:39:31 +0900, Hal Fulton wrote:

> Markus wrote:
>> Where are you going with this?  There seem to be three unrelated things
>> here:
> 
> Well, I have been thinking along the lines of: What if we had a built-in
> ordered indexable collection in Ruby?
> 

What about an association list (Array)?

[["one", 1], ["two", 2], ["three", 3]].assoc("one")
=> ["one", 1]

You could wrap it in a class to have it behave more like a Hash.

>> To see why this seems odd, let me recast your question in terms of
>> arrays:
>> 
>> <analogy>
> 
> [snip]
> 
> Clever analogy, but you're presupposing an unordered arbitrarily indexable
> collection. A hash, like our Hash, is inherently unordered, but I am
> imagining a similar ordered data structure.
> 
> It's more like:
> 
>    x = [1,2]
>    y = [2,1]
>    x == y     # false - we *do* depend on this being false
> 
> I'm envisioning a data structure that has an order, but is otherwise (in
> behavior, not implementation) like our current Hash.
> 
> I don't want to go into detail about what I'm thinking at the moment.
> 
> But I can see where my post was unclear or vague and would raise very
> valid questions in your mind.
> 
> 
> Hal

Regards,
KB