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Ruby Core and Standard Library

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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.

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

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    Let's say that you are writing a text based game and 0:00
    wanted to save the current player's 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 and 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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