Programming Ruby

The Pragmatic Programmer's Guide

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module Marshal


dump load restore

The marshaling library converts collections of Ruby objects into a byte stream, allowing them to be stored outside the currently active script. This data may subsequently be read and the original objects reconstituted. Marshaling is described starting on page 268.

Some objects cannot be dumped: if the objects to be dumped include bindings, procedure objects, instances of class IO, or singleton objects, a TypeError will be raised.

If your class has special serialization needs (for example, if you want to serialize in some specific format), or if it contains objects that would otherwise not be serializable, you can implement your own serialization strategy by defining two methods, _dump and _load:

Method Type Signature Returns
Instance _dump(aDepth) Returns a String
Class _load(aString) Returns a reconstituted Object

The instance method _dump should return a String object containing all the information necessary to reconstitute objects of this class and all referenced objects up to a maximum depth of aDepth (a value of -1 should disable depth checking). The class method _load should take a String and return an object of this class.

class methods
dump dump( anObject [, anIO ] , limit=--1 ) -> anIO

Serializes anObject and all descendent objects. If anIO is specified, the serialized data will be written to it, otherwise the data will be returned as a String. If limit is specified, the traversal of subobjects will be limited to that depth. If limit is negative, no checking of depth will be performed.

class Klass
  def initialize(str)
    @str = str
  def sayHello

o ="hello\n")
data = Marshal.dump(o)
obj = Marshal.load(data)
obj.sayHello "hello\n"

load load( from [, aProc ] ) -> anObject

Returns the result of converting the serialized data in from into a Ruby object (possibly with associated subordinate objects). from may be either an instance of IO or an object that responds to to_str. If proc is specified, it will be passed each object as it is deserialized.

restore restore( from [, aProc ] ) -> anObject

A synonym for Marshal::load .

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at

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