From: Sean O'Dell <sean@...>
Date: 2004-06-13T13:56:46+09:00
Subject: Re: How to ducktype a Hash?

On Saturday 12 June 2004 19:19, Gavin Sinclair wrote:
> On Sunday, June 13, 2004, 10:55:53 AM, Sean wrote:
> >> > Not necessarily.  A database abstraction might act like a hash, but
> >> > wouldn't dump entire tables, which could contain tens of thousands of
> >> > records, as one big Ruby hash.  That isn't positive identification.
> >>
> >> Such an abstraction could give a lazy-loading Hash, as in
> >>
> >>   class DBAbstraction
> >>     def to_hash
> >>       Hash.new { |hash, key|
> >>         hash[key] = expensive_lookup(key)
> >>       }
> >>     end
> >>   end
> >>
> >> So when you call #to_hash in the first place, it's empty.  Each key
> >> you call results in a calculation.  All unbeknownst to the user of the
> >> hash.
> >
> > I don't see how this works.  When you call to_hash, no arguments are
> > provided, so how could you use the key value there?  I've also never seen
> > the block parameter to Hash.new.  Not that this changes anything
> > regarding positive identification of a class' purpose, but it's very
> > interesting.  Is this all new?  My Pragmatic Programmer's Guide must
> > already be far out of date.
>
> Try 'ri Hash.new'.  All will be explained.

No such command.  It doesn't ship with Ruby?  I installed ri as a gem, but it 
installed something called Labyrinth.  Anyway, interesting addition to Hash!

	Sean O'Dell