From: Gavin Sinclair <gsinclair@...>
Date: 2004-06-08T20:32:56+09:00
Subject: Re: How to ducktype a Hash?

Jim Weirich wrote:
> Actually, I was going to write up a proposal but saw a posting
> in ruby-talk:102752 that echoed my idea.  We need a mixin module for
> hashable (similar to Enumerable) that implements the basic functionality
> of hashes on the basis of a small number of primitives.  Then anyone
> needing hash-like behavior would mixin this module and would get a fully
> implemented Hash interface.
>
> Advantages:
>    * Full set of hash methods for the cost of implementing a small
>      number of primitives.
>    * Well defined semantics[1] for all the hash methods
>    * Easy to check test to see if something implements hash-like
>      behavior (obj.is_a?(Hashable)).

I like the idea.  Can you propose some details?  And can it be called Map
rather than Hashable?  I presume you're talking about map semantics,
involving mapping a key to a value, rather than hash semantics, involving
calculating hash codes.

obj.is_a?(Map) reads nicely to me.

> I see a need for something like this for IO as well (eg. Readable,
> Writeable).

That seems less important than the much-discussed-from-all-angles Hash,
but interesting nonetheless.  Again, I'm hungry for details.

Cheers,
Gavin