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Marshal

3:52 with Jason Seifer

The Marshal class in Ruby Core allows you to convert Ruby objects in to a data stream and back again.

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Marshal documentation

Code Samples

Here is our player class with two attributes: name and progress:

class Player
  attr_accessor :name, :progress

  def initialize(name)
    @name = name
  end
end

Using the Marshal library, we can output this player object to a string:

player = Player.new("Jason")
player.progress = 60

player_out = Marshal.dump(player)

puts player_out.inspect

Results in the following:

"\x04\bo:\vPlayer\a:\n@nameI\"\nJason\x06:\x06ET:\x0E@progressiA"

We can then load it later and the object will have the same data:

player_in = Marshal.load(player_out)

puts player_in.inspect

Let's say that you are writing a text based game and 0:00 wanted to save the current players progress. 0:03 How would you do it? 0:06 You would need to take into account the different things. 0:08 You could have to save the player, any items it has, and so on. 0:11 One thing that you can do to save the game state 0:16 is use the Marshal class to save Ruby objects. 0:18 Marshal class in Ruby core, 0:23 allows you to convert Ruby objects into a data stream and back again. 0:25 Let's go ahead a take a look at that now using work spaces. 0:31 Now here's the documentation for the Marshal class. 0:35 Now it says here the Marshalling library converts collections of ruby objects into 0:39 a byte stream, allowing them to be stored outside the currently active script. 0:44 What in the world does this mean? 0:50 Well, this means that you can dump your current ruby 0:52 objects into a string and then that string can be loaded later on. 0:57 Let's go ahead and take a look at this inside of IRB. 1:02 Now I've got this very simple class that I've written called Player. 1:07 It's got attribute accessors for name and progress. 1:10 That's gonna be how far along the player is in the game. 1:14 So I'm gonna go ahead and launch IRB and require the Player class at the same time. 1:17 We can do this by typing IRB -r in the path to 1:23 the file that you'd like to require, -r stands for require. 1:28 So let me go ahead and create a new player. 1:33 Say a player is Player.new. 1:36 Jason and the player.progress is 40, only 40% through the game. 1:42 So now, if I wanted to output this player, 1:50 let's go ahead and head back to the Marshal documentation. 1:54 We could use Marshal.dump and Marshal.load to load these things. 2:02 So I could say the output is equivalent to Marshal.dump(player). 2:09 Now if we look at this we have a string representation. 2:17 Which also contains our variable date. 2:25 Now once we have this out, we could pass this around, right? 2:29 So here's our string. 2:33 Let's go ahead and load it though and 2:35 say Marshal.load(player) and we'll assign this to another variable here. 2:37 And we'll just say this new_player object is equal to loading Marshal.load(output). 2:45 Now if we look at this new_player, it is another object. 2:54 It's got the same data as our other player, 2:59 same progress and same name. 3:05 So, those attributes stayed the same. 3:09 Now we could use this for other object too. 3:11 It's not limited to just classes that we've written and 3:14 if it gets very complicated, we can actually go through and 3:18 serialize our data a little bit differently. 3:22 Now, there are some security considerations when you 3:26 are using the Marshalling library. 3:28 The load method deserializes any class loaded into Ruby, so 3:32 you need to make sure that you trust your data. 3:37 This isn't something that you would want to be loading straight from, for 3:40 example, a form on a web page. 3:44 Try using Marshall on your own now using work spaces. 3:47

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