From: Robert Klemme <bob.news@...>
Date: 2006-03-23T18:13:51+09:00
Subject: Re: Is this a kind of design patterns?

Jim Weirich wrote:
> Robert Klemme wrote:
>> Sam Kong wrote:
>>>     end
>>>         def blue
>>> puts Color.red
>>> puts Color.blue
>>>
>>>
>>> Is this one of design patterns, or just a simple idiom?
>>> It's similar to a factory method pattern but it's not according to the
>>> definition.
>>> Is there any name for it?
>> Since you invoke a class's method "new" like any other method of any
>> other object (no special syntax) you can say with some justification
>> that all classes are basically factories.
>>
>> IMHO your example is not optimal because it wastes resources.  Since
>> Color is immutable anyway constants seem a better choice:
>>
>> Color = Struct.new :r, :g, :b
>> class Color
>>    def to_s
>>      sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
>>    end
>>
>>    RED   = new 0xFF, 0x00, 0x00
>>    BLUE  = new 0x00, 0x00, 0xFF
>>    GREEN = new 0x00, 0xFF, 0x00
>> end
> 
> I was thinking along the same lines, but I do like the method interface 
> (e.g. Color.red over Color::RED).  My suggestion would have been 
> something like:
> 
>   class Color
>     ...
>     class << self
>       def red
>         @red ||= new 255, 0, 0
>       end
>       ...
>     end
>   end

IMHO this is not thread safe.  If you need the method interface, you 
could do something like

class Color
   def self.method_missing(s,*a,&b)
     if a.empty? && b.nil?
       const_get s.to_s.upcase
     else
       super
     end
   end
end

:-)

	robert