From: Stefan Rusterholz <apeiros@...>
Date: 2007-05-28T20:36:39+09:00
Subject: Re: Tricky problem with ===

unknown wrote:
> Hi --
> 
> On Mon, 28 May 2007, Erwin Abbott wrote:
> 
>> time. It's job is to return true if the given time is more than a week
>> and look up the documentation. I agree distinguishing objects by class
>> #old_name and making sure my #name doesn't break any code in that
>> class. I might still break something with a proxy class answering
>> #name, but it won't break the underlying object when it calls name on
>> itself. I think at this point I'll accept that case statements won't
>> work, but I'm going to try a few other things before giving up.
> 
> I was thinking of something like (semi-tested only):
> 
>    module DateComp
>      def <(other)
>        Time.parse(strftime("%m/%d/%y")) < other
>      end
>    end
> 
>    d = Date.new.extend(DateComp)
>    your_method(d)
> 
> That way, you can use duck typing in the method itself, which means
> that you don't have to change the method if you want to provide it
> with other objects; you just have to prepare things on the calling
> end.  You might have to have a more complex mixin for your proxy case,
> but anyway, that's the kind of thing I was thinking about.
> 
> 
> David

Universal Date/Time comparison is indeed difficult as neither your nor 
mine (below) solution attribute for different TimeZones and/or DST.
I'd implement a universal comparison like below:

def <=>(other)
  [year, day_of_year, hour, minute, second] <=> [other.year, 
other.day_of_year, other.hour, other.minute, other.second]
end

Regards
Stefan

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