Subclassing Immutable objects (Time)

ruby-talk
1

How about not sub-classing, and have Time be an implmentation detail
of your class? You can use method_missing to forward all methods
you don't specifically implement to your @time attribute, and you
can be mutable by just replacing your @time.

Sam

Quoteing tone_hole@yahoo.ca, on Thu, Feb 10, 2005 at 10:29:45PM +0900:

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Hi folks,

I've been trying for a while to subclass Time, but i'm hitting some
problems. I tried simply overriding the methods in Time itself but
after about 5 minutes i realized that i needed the old behaviour as
well, so subclassing seems better. I'm hitting the same problems with
wrapping the object as well.

I know this question has been asked before but as far as i can tell they
all seemed to deal with mutable objects (one notable example dealt with
Array which has a nice replace() method available to it)

Because Time is immutable, there are a ton of methods that return new
Time objects (class method parse, instance methods +, and - are the
notable ones since i'm interested in these). So if i write:

class MyTime < Time
end

And do the following:

time = MyTime.parse("00:00:00") # returns Time
time = MyTime.now + 50.0 # returns Time

Now, i could reimplement these methods in MyTime to return MyTime
objects but I'm lost on how to do the conversion without something like
Array's replace() method. If i had it then i could do:

class MyTime < Time

~ def MyTime.parse(str)
~ now.replace(Time::parse(str))
~ end

~ def +(other)
~ replace(Time::+(other))
~ end

end

or something along those lines.

Anyone have any tips?

Thanks,
Derek
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