Sub-classing Fixnum in ruby

Question

So I understand you aren\'t supposed to to directly subclass Fixnum, Float or Integer, as they don\'t have a #new method. Using DelegateClass seems to work though, but is it

Answer 1

You can pretty easily set up a quick forwarding implementation yourself:

class MyNum
  def initialize(number)
    @number = number
  end

  def method_missing(name, *args, &blk)
    ret = @number.send(name, *args, &blk)
    ret.is_a?(Numeric) ? MyNum.new(ret) : ret
  end
end

Then you can add whatever methods you want on MyNum, but you'll need to operate on @number in those methods, rather than being able to call super directly.

Answer 2

Could you not extend FixNum itself? Like...

class Fixnum
  def even?
    self % 2 == 0
  end
end

42.even?

Answer 3

IIRC, the main implementation of Ruby stores Fixnums as immediate values, using some of the low bits of the word to tag it as a Fixnum instead of a pointer to an object on the heap. That's why, on a 32-bit machine, Fixnums are only 29-bits (or whatever it is) instead of a full word.

So because of that, you can't add methods to a single "instance" of Fixnum, and you can't subclass it.

If you're dead-set on having a "Fixnum-like" class, you'll probably have to make a class that has a Fixnum instance variable, and forward method calls appropriately.