Inheritance/Composition

gistfile1.rb

module DBCLibrary
  module Barcodable
    attr_reader :location
    attr_accessor :barcode
  end
end

module DBCLibrary
  class BluRay < LibraryItem
    include Borrowable, Reservable
  end
end

module DBCLibrary
  class Book < LibraryItem
    include Borrowable, Reservable
  end
end

module DBCLibrary
  module Borrowable
    def borrow! who
      @borrowed_by = who
    end

    def borrowed?
      !!@borrowed_by
    end

    def return!
      @borrowed_by = nil
    end
  end
end

# Computers cannot be borrowed
module DBCLibrary
  class Computer < LibraryItem
    include Reservable
  end
end

module DBCLibrary
  class Library
    attr_reader :books, :librarian

    def initialize args={}
      @books     = args[:books]
      @librarian = args[:librarian]
    end
  end
end

module DBCLibrary
  class LibraryItem
    include Barcodable

    def initialize args={}
      @title       = args[:title]
      @description = args[:description]
    end
  end
end

module DBCLibrary
  class Magazine < LibraryItem
    include Borrowable, Reservable
  end
end

module DBCLibrary
  class Photocopier
    include Barcodable
  end
end

# Reference books cannot be borrowed
module DBCLibrary
  class ReferenceBook < LibraryItem
    include Reservable
  end
end

module DBCLibrary
  module Reservable
    def reserve! who
      @reserved_by << who
    end

    def reserved?
      @reserved_by.size > 0
    end

    def unreserve! who
      @reserved_by.delete who
    end
  end
end