From: Ben Giddings <bg-rubytalk@...>
Date: 2003-09-10T01:17:56+09:00
Subject: Re: ANN: MetaTags 1.0

Dave Thomas wrote:
> We could still define the global method
> 
>    Date "date string"
> 
> Which parsed the string, reporting errors for incorrect strings, and 
> then called the constructor with the three integers.
> 
> This approach also allows for memoizing the returned values, which in 
> general you probably shouldn't do with raw constructors.

Hmm...  I think it might be a better idea to create a "memoizer factory" 
or something.  Maybe instead of Date.new you'd say Date.build or 
Date.construct, and instead of passing it a string, you pass it a "memo 
string" or something to indicate it makes sense to memoize the operation.

You could do this by simply having a 'date_memoizer.rb' file with 
contents like:

class Date
   def self.construct(arg)
     @@memo_hash ||= Hash.new

     if arg.respond_to(:memoizable)
       ...
     else
       ...
     end
   end
end

The main problems I see are that:
* Date() looks like a constructor for a Date object, if you're not 
familliar with Ruby's constructor syntax, and for anybody reading the 
code that could be a bad thing.  It might seem like there are two kinds 
of constructors in Ruby, one for initializing from data, one for 
initializing from strings.
* It's not obvious that Date() has any connection to memoization
* I have an aversion to top-level functions.  ;)

Ben