From: Daniel Vartanov <daniel.vartanov@...>
Date: 2008-11-04T18:52:36+09:00
Subject: Conditional overriding of operators

Hello!

I am trying to replace .+ operator of Numeric class if and only if
argument (summand) is my own class.

To be more specific: I am writing geometry module in Ruby and need to
implement vector-number multiplication so that both:

2 * vector
vector * 2

work well.

Therefore I need to replace .+ method of Numeric without spoiling
arithmetical operations with other classes. It is clear, that in case of
inheritance we can just write:

class MyNumeric < Numeric
  def +(object)
    super(object) unless object.kind_of?(Vector)

    # vector-number multiplication here...
  end
end

But, of course, we need a replacement here. How to implement it?

class Numeric
  def +(vector)
    unless vector.kinf_of?(Vector)
      # What to write here??!
    end

    # vector-number multiplication here...
end
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