From: Robert Klemme <shortcutter@...>
Date: 2007-02-05T07:35:08+09:00
Subject: Re: Inheriting from Fixnum

On 04.02.2007 17:13, gga wrote:
>> I try differently: what kind of class do you want to implement?  Why do
>> you think you need to inherit?  What capabilities should instances of
>> your class have?
> 
> Simple.  I want a Fixnum.   I don't want to pollute Fixnum's namespace
> and I don't want a Fixnum to automatically be promoted to my class,
> while at the same time, my class should be compatible with ALL of
> fixnum methods (odd? even?, etc).
> Think of a Year class (yes, I know there's Date and DateTime -- my
> class is not exactly this but will do as an example).  A year is
> represented by a Fixnum, but it is not a Fixnum.
> Yet I expect all Fixnum operations to work on it, returning a new Year
> in case of additions, etc.  I also don't want a normal Fixnum to be
> treated as a year without a conversion function or instantiation thru
> Year.new().  Also, I want to have a lof of conversion functions within
> Year that are not applicable to Fixnum ( to_months, to_days, etc ).

Is it a year of the century or years difference?  How would you 
implement to_days? I don't think this is worth another class - and btw. 
there are classes for date and time handling in Ruby which support all 
the math you typically need.  Plus, you can also define methods in a 
more functional way (i.e. def year_to_months(year) etc.).

> Right now, to do that, I have to actually recreate all of the methods
> in Fixnum/Numeric/etc. while if I was inheriting from it, I would only
> have to recreate half of them or less or rely on method_missing
> (yuck).

You can still use delegator...

> The ruby source code contains no explanation for the removal of new.
> That's why I'm wondering what the reasoning behind this was.  It does
> not seem to be technical limitation in the ruby interpreter.
> Currently, it does not make much sense to me.

It's an internal optimization.  Fixnums do not have to be created and 
they never have to be GC'ed.  This goes a long way to make math faster 
than it would be with ordinary objects (at least for Fixnums).

Regards

	robert