From: Logan Capaldo <logancapaldo@...>
Date: 2007-02-05T12:52:26+09:00
Subject: Re: Inheriting from Fixnum

On Mon, Feb 05, 2007 at 10:10:05AM +0900, gga wrote:
 
> I can (and as I said, I have already), it is just pretty inelegant and
> inefficient.  Taking care of kind_of? and similar is pretty messy (but
> needed as I do want to have Range of frames, for example).
> Therefore, I want to know the reason of WHY I am forced to use a
> delegator for deriving one of the most basic classes possible.  So
> far, I don't know why I need to go through such a cumbersome approach.
> 
1) Fixnum and Bignum are implementation details. If you want to
inherit from anything it should be from Integer. Programmer's that add
methods to just Fixnum are likely making an error.

2) There is no need to "take care of" kind_of? for Ranges.

Ranges rely on #succ and #<=>, that's it.
% irb
irb(main):001:0> class Frame
irb(main):002:1>   def initialize( value )
irb(main):003:2>     @value = value
irb(main):004:2>   end
irb(main):005:1>   
irb(main):006:1*   def succ
irb(main):007:2>     Frame.new( @value.succ )
irb(main):008:2>   end
irb(main):009:1>   
irb(main):010:1*   def <=>(other)
irb(main):011:2>     @value <=> other.instance_variable_get("@value")
irb(main):012:2>   end
irb(main):013:1>   
irb(main):014:1*   include Comparable
irb(main):015:1> end
=> Frame
irb(main):016:0> start = Frame.new(0)
=> #<Frame:0x31dd3c @value=0>
irb(main):017:0> stop = Frame.new(5)
=> #<Frame:0x31ae20 @value=5>
irb(main):018:0> (start..stop).to_a
=> [#<Frame:0x31dd3c @value=0>, #<Frame:0x318684 @value=1>, #<Frame:0x31865c @value=2>, #<Frame:0x318634 @value=3>, #<Frame:0x31860c @value=4>, #<Frame:0x3185e4 @value=5>]
irb(main):019:0> (start..stop).each { |x| p x }
#<Frame:0x31dd3c @value=0>
#<Frame:0x314020 @value=1>
#<Frame:0x313f94 @value=2>
#<Frame:0x313f44 @value=3>
#<Frame:0x313ef4 @value=4>
#<Frame:0x313ea4 @value=5>
=> #<Frame:0x31dd3c @value=0>..#<Frame:0x31ae20 @value=5>
irb(main):020:0> (start..stop).include? Frame.new(3)
=> true
irb(main):021:0> (start..stop).include? Frame.new(9)
=> false

3) The reason you are forced to use a delegator to "derive" from one of
the most basic classes possible is because it is one of the most basic
classes possible. A Fixnum is a primitive. Inheriting from it is akin to
trying to implement arrays in C w/o using arrays. (Note that saying
"well I can do it in python" doesn't hold water, as python selected
different primitives)