From: Philipp Meier <meier@...>
Date: 2002-09-20T02:00:35+09:00
Subject: Re: subclassing Integer


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On Fri, Sep 20, 2002 at 01:20:35AM +0900, John Tromp wrote:
> I'm writing a state space search program where each state can be consisely
> described by an Integer. I need these states to have several new methods.
>=20
> I can either
> 1) create a new class with an Integer attribute
> or
> 2) try to subclass Integer

Subclassing might give you undesired effects with return types. Example:

class Cart < Array
	def total
		sum =3D 0
		each do |product|
			sum +=3D product.price
		end
	end
end

class Product
	attr_reader :price
	def initialize(price)
		@price=3Dprice
	end
end

c =3D Cart.new()
c << Product.new(5)
c << Product.new(10)
c.total    # =3D> 15

c +=3D [Product.new(7)]
c.total    # NameError: undefined method `total' for #<Array:0x402709e8>


-billy.

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