From: Gavin Sinclair <gsinclair@...>
Date: 2004-06-13T08:48:49+09:00
Subject: Re: How to ducktype a Hash?

On Sunday, June 13, 2004, 3:30:38 AM, Sean wrote:

> On Saturday 12 June 2004 04:23, Rene van Bevern wrote:
>> Sean O'Dell wrote:
>> > So, how do I positively identify when an object is a hash or at least
>> > behaves like a hash?
>>
>> Use the method #to_hash instead. All hash-like objects should be able to
>> give a hash-representation of themselves.

> 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.

Gavin