From: Hal Fulton <hal9000@...>
Date: 2006-08-13T15:31:08+09:00
Subject: A use case for an ordered hash

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.


Hal