Object Serialization

<Mutable Immutable Objects | TOC | Modules/Mixins >

Java features the ability to serialize objects, letting you store them somewhere and reconstitute them when needed. Ruby calls this kind of serialization marshaling.

We will write a basic class p051gamecharacters.rb just for testing marshalling.

# p051gamecharacters.rb
class GameCharacter
  def initialize(power, type, weapons)
    @power = power
    @type = type
    @weapons = weapons
  end
  attr_reader :power, :type, :weapons
end

The program p052dumpgc.rb creates an object of the above class and then uses Marshal.dump to save a serialized version of it to the disk.

# p052dumpgc.rb
require_relative 'p051gamecharacters'
gc = GameCharacter.new(120, 'Magician', ['spells', 'invisibility'])
puts "#{gc.power} #{gc.type}"
gc.weapons.each do |w|
  puts w
end

File.open('game', 'w+') do |f|
  Marshal.dump(gc, f)
end

The program p053loadgc.rb uses Marshal.load to read it in.

# p053loadgc.rb
require_relative 'p051gamecharacters'
File.open('game') do |f|
  @gc = Marshal.load(f)
end

puts "#{@gc.power} #{@gc.type}"
@gc.weapons.each do |w|
  puts w
end

Marshal only serializes data structures. It can't serialize Ruby code (like Proc objects), or resources allocated by other processes (like file handles or database connections). Marshal just gives you an error when you try to serialize a file.

Note: The Ruby Logo is Copyright (c) 2006, Yukihiro Matsumoto. I have made extensive references to information, related to Ruby, available in the public domain (wikis and the blogs, articles of various Ruby Gurus), my acknowledgment and thanks to all of them. Much of the material on rubylearning.github.io and in the course at rubylearning.org is drawn primarily from the Programming Ruby book, available from The Pragmatic Bookshelf.

<Mutable Immutable Objects | TOC | Modules/Mixins >