Objectmancy is a way to convert Hashes to Objects of your choosing without having to inherit from anything, primitive or otherwise. You need only include the appropriate module and define your attributes.

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Add this line to your application's Gemfile:

gem 'objectmancy'

And then execute:

$ bundle

Or install it yourself as:

$ gem install objectmancy


To include Objectable, you may include Objectmancy as well for easier consumption.


You can include Objectmancy into your class to gain both Objectable and Hashable functionality.


Objectmancy::Objectable is the Module to mixin in order to consume the abilities. It works with the cooperation of three methods .attribute, .multiples and .initialize.


Objectable provides an .initialize method for your object that you can use at any time. You may override with your own and call super and pass it your values to create your object. You may also define a separate class method to use with Objectable. However, preferably, you will keep and use Objectable's .initialize method and make use of the before_initialize or after_initialize callbacks if you need custom behavior.


By default, your new object's values will be set to whatever the associated key is in the base hash. You can specify a :type option which lets you use either a Class of your choosing to create the object, or a Symbol representing a type that Objectmancy knows about. By default, Objectable will call new on your passed in type and pass the value of the hash to it. You may set the :objectable option to provide a different method to call on the :type value. The value of the hash is still the only argument passed.


multiples behaves in much the same way, except a :type option is required. .multiples is intended for Arrays of objects which need special attention (i.e., custom defined types or objects of a type supported by Objectmancy)


The following is an extensive example of a set of classes built to consume Objectmancy::Objectable in all of its basic ways. This is taken from the tests, with comments added as guidance. Skipping ahead to the TestObject definition will provide the most value.

class Book
  include Objectmancy::Objectable

  # These are basic attributes. They can be anything; your new object
  # will have these attributes set to whatever key this is in the Hash.
  attribute :title
  attribute :author

class Cat
  attr_reader :name

  # Just to notice that you could create anything, not necessarily what the 
  # key explicitly is.
  def initialize(name)
    @name = name

  def ==(other)
    self.class == other.class &&
      name == other.name

class Game
  attr_reader :title, :developer

  def initialize(title, developer)
    @title = title
    @developer = developer

  # An arbitrary method defined to create this object from something other
  # than new. This allows you to avoid the "shimming" if you prefer, and makes 
  # it possible to override initialize and still use Objectable, providing 
  # some from of backwards compatibility.
  def self.from_string(str)
    values = str.split '/'
    new(values.first, values.last)

  def ==(other)
    self.class == other.class &&
      title == other.title &&
      developer == other.developer

class TestObject
  include Objectmancy::Objectable

  # Random attr_reader used to test that the callbacks were in fact invoked.
  attr_reader :before_init, :after_init

  attribute :name

  # Usage of a supported, built-in type
  attribute :update_date, type: :datetime

  # Usage of a user-defined type using Objectable
  attribute :book, type: Book

  # Usage of a user-defined type with new method 
  attribute :pet, type: Cat

  # USage of a user-defined type with a custom objectable method
  attribute :video_game, type: Game, objectable: :from_string

  # Basic array of integers
  attribute :primes

  # Array of objects to be parsed into a supported type
  multiples :birth_dates, type: :datetime

  # Array of objects into a user-defined type using Objectable
  multiples :library, type: Book

  # Array of objects into a user-defined type using new
  multiples :menagerie, type: Cat

  # Array of objects into a user-defined type using a custom objectable method
  multiples :board_games, type: Game, objectable: :from_string

  # Callback method used at the beginning of the Objectable.initialize method. 
  # This is called before any attributes are set.
  def before_initialize
    @before_init = :before_set

  # Callback method used at the end of the Objectable.initialize method.
  # This is called after all attributes are set.
  def after_initialize
    @after_init = :after_set


Objectmancy::Hashable is a mixin for making an object easier to convert into a Hash. This defines Hashable#hashify on an object. This should not be overridden. You must define the attributes to be Hashified using the .attribute or .multiples method for Arrays of special objects. Objects requiring .multiples for a collection are those with a supported type or those with a custom :hashable method. When defining, it shoud follow this pattern (method name of #hash_me aside):

class Kitten
  def iniitialize(name)
    @name = name

  def hash_me
    "#{name} is a cat"

class Foobar
  include Objectmancy::Hashable

  multiples :fizzbangs, hashable: :hash_me

f = Foobar.new
f.fizzbangs = [Kitten.new('Tux'), Kitten.new('Socks')]
f.hashify # => { fizzbangs: ['Tux is a cat', 'Socks is a cat'] }

If no custom handling is provided for non-standard value (string, number, array, hash, etc...), either through a defined method or via including Hashable, then the output value will be the object definition (typically something like #<Foobar:0x007ffb168b3760>), so it's good to define a method of some kind.

Supported types

Currently supported known types with built-in parsing into non-standard objects:


After checking out the repo, run bundle install to install dependencies. Then, run bundle exec rake test to run the tests. You can run bundle exec rubocop to run the rubocop static analysis tool.

To install this gem onto your local machine, run bundle exec rake install, or you can use bundle exec pry, as I've included pry in the Gemfile. Please feel free to comment this out if you prefer a different debugger.


Bug reports and pull requests are welcome on GitHub at https://github.com/jon2992/objectmancy. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.