Subclassing Immutable objects (Time)

ruby-talk
1

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

2

In my MutableTime class [1], I wrapped Time, rather than inheriting from it, and used method_missing to pass functions along to time.

Tiny snippets:

class MutableTime
  include Comparable

  def initialize( dateString_Seconds_Time_orYear = nil , *dateTimePieces )
    #...
    @t=Time.now
  end

  def method_missing(meth, *args, &block) # :nodoc:
    @t.send(meth, *args, &block)
  end

  def date=(n)
    @t+=(n-date)*86400;
  end

  def +(n)
    (d=self.dup).date+=n
    d;
  end
end

[1] File: MutableTime.rb

···

On Feb 10, 2005, at 6:29 AM, Derek Wyatt wrote:

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.

3

Gavin,

This looks very interesting -- thanks for the pointer. I'll take a look
at it and see how i can adapt it to my situation.

(Sam, you were headed right along the same path so this certainly seems
to be the right way)

Thanks again,
Derek

Gavin Kistner wrote:

···

On Feb 10, 2005, at 6:29 AM, Derek Wyatt wrote:

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.

In my MutableTime class [1], I wrapped Time, rather than inheriting from
it, and used method_missing to pass functions along to time.

Tiny snippets:

class MutableTime
    include Comparable

    def initialize( dateString_Seconds_Time_orYear = nil ,
*dateTimePieces )
        #...
        @t=Time.now
    end

    def method_missing(meth, *args, &block) # :nodoc:
        @t.send(meth, *args, &block)
    end

    def date=(n)
        @t+=(n-date)*86400;
    end

    def +(n)
        (d=self.dup).date+=n
        d;
    end
end

[1] File: MutableTime.rb