From: James Edward Gray II <james@...>
Date: 2006-08-14T00:27:07+09:00
Subject: Re: A use case for an ordered hash

On Aug 13, 2006, at 3:25 AM, Robert Klemme wrote:

> Hal Fulton wrote:
>> There have been numerous occasions when I wanted an
>> ordered hash, but usually I can't remember to write
>> them down.
>> Here's just one.
>> Once I wanted a "dynamic case statement" of sorts.
>> I wanted to use procs as values in a hash. Something
>> like:
>>    actions = { /abcd/  => lambda { do_this },
>>                /xyz/   => lambda { do_that },
>>                /abc/   => lambda { other }}
>> Then I could just iterate through the keys looking
>> for a match, then use that key to find the associated
>> proc and call it.
>> However, I quickly noticed that this is no good. The
>> order of iteration is unpredictable. So I couldn't
>> guarantee that (for example) /abcd/ would be tested
>> before /abc/, and so on.
>> So yeah, I ended up using an array of arrays. But it
>> just felt wrong.
>
> To me a Hash feels wrong.  Why?  Because you don't make any use of  
> hash properties for fast lookup.  You just iterate in plain order.

He *is* making use of a Hash property.  He wants the keys to be  
unique.  None of the other solutions shown in this thread have  
addressed that.

James Edward Gray II