Hashie is a simple collection of useful Hash extensions.
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Note: This documentation is for the unreleased version 2.0 of Hashie. See the 1-1-stable branch for documentation of the released version.


Hashie is a growing collection of tools that extend Hashes and make them more useful.


Hashie is available as a RubyGem:

gem install hashie

Hash Extensions

New to version 2.0 of Hashie, the library has been broken up into a number of atomically includeable Hash extension modules as described below. This provides maximum flexibility for users to mix and match functionality while maintaining feature parity with earlier versions of Hashie.

Any of the extensions listed below can be mixed into a class by include-ing Hashie::Extensions::ExtensionName.


Coercions allow you to set up "coercion rules" based either on the key or the value type to massage data as it's being inserted into the Hash. Key coercions might be used, for example, in lightweight data modeling applications such as an API client:

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :user, User

user_hash = {:name => "Bob"}
Tweet.new(:user => user_hash)
# => automatically calls User.coerce(user_hash) or
#    User.new(user_hash) if that isn't present.

Value coercions, on the other hand, will coerce values based on the type of the value being inserted. This is useful if you are trying to build a Hash-like class that is self-propagating.

class SpecialHash < Hash
  include Hashie::Extensions::Coercion
  coerce_value Hash, SpecialHash

  def initialize(hash = {})
    hash.each_pair do |k,v|
      self[k] = v


The KeyConversion extension gives you the convenience methods of symbolize_keys and stringify_keys along with their bang counterparts. You can also include just stringify or just symbolize with Hashie::Extensions::StringifyKeys or Hashie::Extensions::SymbolizeKeys.


The MergeInitializer extension simply makes it possible to initialize a Hash subclass with another Hash, giving you a quick short-hand.


The MethodAccess extension allows you to quickly build method-based reading, writing, and querying into your Hash descendant. It can also be included as individual modules, i.e. Hashie::Extensions::MethodReader, Hashie::Extensions::MethodWriter and Hashie::Extensions::MethodQuery

class MyHash < Hash
  include Hashie::Extensions::MethodAccess

h = MyHash.new
h.abc = 'def'
h.abc  # => 'def'
h.abc? # => true


This extension can be mixed in to instantly give you indifferent access to your Hash subclass. This works just like the params hash in Rails and other frameworks where whether you provide symbols or strings to access keys, you will get the same results.

A unique feature of Hashie's IndifferentAccess mixin is that it will inject itself recursively into subhashes without reinitializing the hash in question. This means you can safely merge together indifferent and non-indifferent hashes arbitrarily deeply without worrying about whether you'll be able to hash[:other][:another] properly.

DeepMerge (Unimplemented)

This extension will allow you to easily include a recursive merging system to any Hash descendant.


Mash is an extended Hash that gives simple pseudo-object functionality that can be built from hashes and easily extended. It is designed to be used in RESTful API libraries to provide easy object-like access to JSON and XML parsed hashes.


mash = Hashie::Mash.new
mash.name? # => false
mash.name # => nil
mash.name = "My Mash"
mash.name # => "My Mash"
mash.name? # => true
mash.inspect # => <Hashie::Mash name="My Mash">

mash = Mash.new
# use bang methods for multi-level assignment
mash.author!.name = "Michael Bleigh"
mash.author # => <Hashie::Mash name="Michael Bleigh">

Note: The ? method will return false if a key has been set to false or nil. In order to check if a key has been set at all, use the mash.key?('some_key') method instead.


Dash is an extended Hash that has a discrete set of defined properties and only those properties may be set on the hash. Additionally, you can set defaults for each property. You can also flag a property as required. Required properties will raise an execption if unset.


class Person < Hashie::Dash
  property :name, :required => true
  property :email
  property :occupation, :default => 'Rubyist'

p = Person.new # => ArgumentError: The property 'name' is required for this Dash.

p = Person.new(:name => "Bob")
p.name # => 'Bob'
p.name = nil # => ArgumentError: The property 'name' is required for this Dash.
p.email = 'abc@def.com'
p.occupation   # => 'Rubyist'
p.email        # => 'abc@def.com'
p[:awesome]    # => NoMethodError
p[:occupation] # => 'Rubyist'


A Trash is a Dash that allows you to translate keys on initialization. It is used like so:

class Person < Hashie::Trash
  property :first_name, :from => :firstName

This will automatically translate the firstName key to first_name when it is initialized using a hash such as through:

Person.new(:firstName => 'Bob')


Clash is a Chainable Lazy Hash that allows you to easily construct complex hashes using method notation chaining. This will allow you to use a more action-oriented approach to building options hashes.

Essentially, a Clash is a generalized way to provide much of the same kind of "chainability" that libraries like Arel or Rails 2.x's named_scopes provide.


c = Hashie::Clash.new
c.where(:abc => 'def').order(:created_at)
c # => {:where => {:abc => 'def}, :order => :created_at}

# You can also use bang notation to chain into sub-hashes,
# jumping back up the chain with _end!
c = Hashie::Clash.new
c # => {:where => {:abc => 'def', :ghi => 123}, :order => :created_at}

# Multiple hashes are merged automatically
c = Hashie::Clash.new
c.where(:abc => 'def').where(:hgi => 123)
c # => {:where => {:abc => 'def', :hgi => 123}}

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add tests for it. This is important so I don't break it in a future version unintentionally.
  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  • Send me a pull request. Bonus points for topic branches.


  • Michael Bleigh


Copyright (c) 2009-2011 Intridea, Inc. (http://intridea.com/). See LICENSE for details.