From: mark sparshatt <msparshatt@...>
Date: 2003-09-12T04:12:31+09:00
Subject: Re: ANN: MetaTags 1.0

Richard Kilmer wrote:

>
> On Thursday, September 11, 2003, at 01:31  AM, Martin DeMello wrote:
>
>> Dave Thomas <Dave@pragprog.com> wrote:
>>
>>>
>>> Or perhaps even using the '>>' operator (as in 'becomes' or 'inject
>>> into')
>>>
>>>     c = "one hump or two" >> Caml
>>
>>
>> Nice! And perhaps the other way around too - I notice that Class#<< is
>> undefined.
>>
>> c = Caml << "one hump or two" (read 'from')
>>
>> martin
>>
>
> Oh my...improving on perfection!  You could make this type-selectable:
>
> class Date
>   def self.__String(string)
>     puts "String factory"
>     Date.new
>   end
>   def self.__Fixnum(millis)
>     puts "Fixnum factory"
>     Date.new
>   end
> end
>
> class Class
>   def <<(object)
>     sym = "__#{object.class}".intern
>     return send(sym, object) if respond_to?(sym)
>     return nil
>   end
> end
>
> d = Date << "String"
> d = Date << 1234543
>
> The generic factory pattern!
>
>
I like the general idea. But I'd prefer it if the << operator raised an 
error if the type isn't supported instead of returning null

Something like

class Class
  def <<(object)
    sym = "__#{object.class}".intern
    return send(sym, object) if respond_to?(sym)
    raise TypeError
  end
end

Best regards

Mark Sparshatt