helper.rb

module Ogre
    def assert
      raise "Assertion failed !" unless yield if $DEBUG
    end
end

vector2.rb

require_relative 'helper'

module Ogre
    class Vector2
        include Ogre
        attr_accessor :x, :y

        def initialize(x, y)
            @x = x.to_f
            @y = y.to_f
        end

        def Vector2.scalar(scale)
            new(scale, scale)
        end

        def Vector2.coordinates(list)
            new(list[0], list[1])
        end

        def swap(other)
            raise "The parameter is not an instance of Vector2." unless other.respond_to? 'swap' and other.instance_of? Vector2

            x, y = @x, @y
            @x, @y = other.x, other.y
            other.x, other.y = x, y
        end

        def [](i)
            assert {i.to_i < 2}
            case i
            when 0
                x
            when 1
                y
            end
        end

        def to_s
            "%.2f, %.2f" % [@x, @y]
        end
    end
end

v2 = Ogre::Vector2.new(0.0, 1.0)
v3 = Ogre::Vector2.scalar(3)
puts 'before'
p v2
p v3
v2.swap v3
puts 'after'
p v2
p v3

p v2[0]
p v3[1]