Inheritance.rb

# Ruby Sample program from www.sapphiresteel.com

# illustrates how to creating descendent objects
# reading and writing attributes
# object (instance) variables
# class variables

	# Thing
  class Thing
    @@num_things = 0 # class variable

    attr_reader( :name, :description )
    attr_writer( :description )

    def initialize( aName, aDescription )
      @name         = aName
      @description  = aDescription
      @@num_things +=1  # increment @@num_things
    end

    def to_s # override default to_s method
      return "(Thing.to_s):: The #{@name} Thing is #{@description}"
    end

    def show_classvars
      return "There are #{@@num_things} Thing objects in this game"
    end

  end

# Room
  class Room < Thing
    # TODO: Add Room-specific behaviour
  end

# Treasure
  class Treasure < Thing
    attr_reader :value
    attr_writer :value

    def initialize( aName, aDescription, aValue )
        super( aName, aDescription )
        @value = aValue
    end
  end


  # Map
  class Map
  # @rooms will be an array - an ordered list
  # of Room objects
    def initialize( someRooms )
      @rooms = someRooms
    end

    # The to_s method iterates over all the Room objects in @rooms
    # and prints information on each. We'll come back to look at the
    # implementation of this method later on
    def to_s
      @rooms.each {
        |a_room|
        puts(a_room)
      }
    end

  end

# First create a few objects
#   i) Treasures
t1 = Treasure.new("Sword", "an Elvish weapon forged of gold",800)
t2 = Treasure.new("Dragon Horde", "a huge pile of jewels", 550)
#   ii) Rooms
room1 = Room.new("Crystal Grotto", "A glittery cavern")
room2 = Room.new("Dark Cave", "A gloomy hole in the rocks")
room3 = Room.new("Forest Glade", "A verdant clearing filled with shimmering light")
#   iii) a Map - which is an array containing the Rooms just created
mymap = Map.new([room1,room2,room3])
# Now let's take a look at what we've got...
puts "\nLet's inspect the treasures..."
puts "This is the treasure1: #{t1.inspect}"
puts "This is the treasure2: #{t2.inspect}"
puts "\nLet's try out the Thing.to_s method..."
puts "Yup, treasure 2 is #{t2.to_s}"
puts "\nNow let's see how our attribute accessors work"
puts "We'll evaluate this:"
puts 't1 name=#{t1.name}, description=#{t1.description}, value=#{t1.value}'
puts "t1 name=#{t1.name}, description=#{t1.description}, value=#{t1.value}"
puts "\nNow we'll assign 100 to t1.value and alter t1.description..."
t1.value = 100
t1.description << " (now somewhat tarnished)" # note << appends specified string to existing string
puts "t1 (NOW) name=#{t1.name}, description=#{t1.description}, value=#{t1.value}"
puts "\nLet's take a look at room1..."
puts "room1 name=#{room1.name}, description=#{room1.description}"
puts "\nAnd the map..."
puts "mymap = #{mymap.to_s}"
puts "\nFinally, let's check how many Thing objects we've created..."
puts( t1.show_classvars )

# As an exercise, try adding a class variable to the Map class to maintain
# a count of the total number of rooms that have been created