Mars Rover code kata

3_mars_rover.rb

class Rover
  class InvalidDirection < StandardError
    def message
      'Vertigoooooo!'
    end
  end

  VALID_DIRECTIONS = %i(north south east west).freeze

  attr_accessor :ns_coordinates, :ew_coordinates, :direction

  def initialize(direction: :north, ns_coordinates: 0, ew_coordinates: 0)
    @direction = direction
    @ns_coordinates = ns_coordinates
    @ew_coordinates = ew_coordinates
  end

  def move
    case direction
    when :north
      @ns_coordinates += 1
    when :south
      @ns_coordinates -= 1
    when :west
      @ew_coordinates += 1
    when :east
      @ew_coordinates -= 1
    else
      fail InvalidDirection
    end
  end

  def turn(towards)
    fail InvalidDirection unless VALID_DIRECTIONS.include?(towards)
    @direction = towards
  end

  def coordinates
    [ns_coordinates, ew_coordinates]
  end
end

run.rb

require './3_mars_rover.rb'

rover = Rover.new
7.times { rover.move }
rover.turn(:east)
3.times { rover.move }
rover.turn(:south)
2.times { rover.move }
rover.turn(:west)
rover.move

puts "Rover is at #{rover.coordinates} facing #{rover.direction}"

til.md

1. #attr_accessor gives us the combined advantages of both #attr_reader and #attr_writer. Cool! Wait, += don't seem to work as expected! What's happening behind the scenes, does it not unfold into = and +?

2. How do we convey the meaning of coordinates in a way that doesn't require the user of our interface to have knowledge of the code within? Is it a Cartesian plane? Both Nick and I started with the same assumption. But Mark's background in building video games drove his decision on coordinates in quite a different direction. Both Tessa and Haani, based on their frontend development expertise, mentioned that even SVG versus canvas consider coordinates differently. Imagine that!

3. What happens when you're passing a constant as the default value upon initialization? I was surprised to see that multiple instances actually reference the same object in memory. So when one changes, this ripples to the other instances as well. Definitely not what I expected, and definitely not the desired behaviour in this case.