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

Table of Contents


Hashie is available as a RubyGem:

$ gem install hashie

Stable Release

You're reading the documentation for the stable release of Hashie, v5.0.0.

Hash Extensions

The library is broken up into a number of atomically includable 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.


Hashie has a built-in logger that you can override. By default, it logs to STDOUT but can be replaced by any Logger class. The logger is accessible on the Hashie module, as shown below:

# Set the logger to the Rails logger
Hashie.logger = Rails.logger


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
  include Hashie::Extensions::MergeInitializer
  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

Coercing Collections

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :mentions, Array[User]
  coerce_key :friends, Set[User]

user_hash = { name: "Bob" }
mentions_hash= [user_hash, user_hash]
friends_hash = [user_hash]
tweet = Tweet.new(mentions: mentions_hash, friends: friends_hash)
# => automatically calls User.coerce(user_hash) or
#    User.new(user_hash) if that isn't present on each element of the array

tweet.mentions.map(&:class) # => [User, User]
tweet.friends.class # => Set

Coercing Hashes

class Relation
  def initialize(string)
    @relation = string

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :relations, Hash[User => Relation]

user_hash = { name: "Bob" }
relations_hash= { user_hash => "father", user_hash => "friend" }
tweet = Tweet.new(relations: relations_hash)
tweet.relations.map { |k,v| [k.class, v.class] } # => [[User, Relation], [User, Relation]]
tweet.relations.class # => Hash

# => automatically calls User.coerce(user_hash) on each key
#    and Relation.new on each value since Relation doesn't define the `coerce` class method

Coercing Core Types

Hashie handles coercion to the following by using standard conversion methods:

type method
Integer #to_i
Float #to_f
Complex #to_c
Rational #to_r
String #to_s
Symbol #to_sym

Note: The standard Ruby conversion methods are less strict than you may assume. For example, :foo.to_i raises an error but "foo".to_i returns 0.

You can also use coerce from the following supertypes with coerce_value:

  • Integer
  • Numeric

Hashie does not have built-in support for coercing boolean values, since Ruby does not have a built-in boolean type or standard method for coercing to a boolean. You can coerce to booleans using a custom proc.

Coercion Proc

You can use a custom coercion proc on either #coerce_key or #coerce_value. This is useful for coercing to booleans or other simple types without creating a new class and coerce method. For example:

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :retweeted, ->(v) do
    case v
    when String
      !!(v =~ /\A(true|t|yes|y|1)\z/i)
    when Numeric
      v == true

A note on circular coercion

Since coerce_key is a class-level method, you cannot have circular coercion without the use of a proc. For example:

class CategoryHash < Hash
  include Hashie::Extensions::Coercion
  include Hashie::Extensions::MergeInitializer

  coerce_key :products, Array[ProductHash]

class ProductHash < Hash
  include Hashie::Extensions::Coercion
  include Hashie::Extensions::MergeInitializer

  coerce_key :categories, Array[CategoriesHash]

This will fail with a NameError for CategoryHash::ProductHash because ProductHash is not defined at the point that coerce_key is happening for CategoryHash.

To work around this, you can use a coercion proc. For example, you could do:

class CategoryHash < Hash
  # ...
  coerce_key :products, ->(value) do
    return value.map { |v| ProductHash.new(v) } if value.respond_to?(:map)



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.

Hashie also has a utility method for converting keys on a Hash without a mixin:

Hashie.symbolize_keys! hash # => Symbolizes all string keys of hash.
Hashie.symbolize_keys hash # => Returns a copy of hash with string keys symbolized.
Hashie.stringify_keys! hash # => Stringifies keys of hash.
Hashie.stringify_keys hash # => Returns a copy of hash with keys stringified.


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


The MethodAccessWithOverride extension is like the MethodAccess extension, except that it allows you to override Hash methods. It aliases any overridden method with two leading underscores. To include only this overriding functionality, you can include the single module Hashie::Extensions::MethodOverridingWriter.

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

class MyOverridingHash < Hash
  include Hashie::Extensions::MethodAccessWithOverride

non_overriding = MyHash.new
non_overriding.zip = 'a-dee-doo-dah'
non_overriding.zip #=> [[['zip', 'a-dee-doo-dah']]]

overriding = MyOverridingHash.new
overriding.zip = 'a-dee-doo-dah'
overriding.zip   #=> 'a-dee-doo-dah'
overriding.__zip #=> [[['zip', 'a-dee-doo-dah']]]


The MethodOverridingInitializer extension will override hash methods if you pass in a normal hash to the constructor. It aliases any overridden method with two leading underscores. To include only this initializing functionality, you can include the single module Hashie::Extensions::MethodOverridingInitializer.

class MyHash < Hash

class MyOverridingHash < Hash
  include Hashie::Extensions::MethodOverridingInitializer

non_overriding = MyHash.new(zip: 'a-dee-doo-dah')
non_overriding.zip #=> []

overriding = MyOverridingHash.new(zip: 'a-dee-doo-dah')
overriding.zip   #=> 'a-dee-doo-dah'
overriding.__zip #=> [[['zip', 'a-dee-doo-dah']]]


This extension can be mixed in to your Hash subclass to allow you to use Strings or Symbols interchangeably as keys; similar to the params hash in Rails.

In addition, IndifferentAccess will also inject itself into sub-hashes so they behave the same.

class MyHash < Hash
  include Hashie::Extensions::MergeInitializer
  include Hashie::Extensions::IndifferentAccess

myhash = MyHash.new(:cat => 'meow', 'dog' => 'woof')
myhash['cat'] # => "meow"
myhash[:cat]  # => "meow"
myhash[:dog]  # => "woof"
myhash['dog'] # => "woof"

# Auto-Injecting into sub-hashes.
myhash['fishes'] = {}
myhash['fishes'].class # => Hash
myhash['fishes'][:food] = 'flakes'
myhash['fishes']['food'] # => "flakes"

To get back a normal, not-indifferent Hash, you can use #to_hash on the indifferent hash. It exports the keys as strings, not symbols:

myhash = MyHash.new
myhash["foo"] = "bar"
myhash[:foo]  #=> "bar"

normal_hash = myhash.to_hash
myhash["foo"]  #=> "bar"
myhash[:foo]  #=> nil


This extension can be mixed in to silently ignore undeclared properties on initialization instead of raising an error. This is useful when using a Trash to capture a subset of a larger hash.

class Person < Trash
  include Hashie::Extensions::IgnoreUndeclared
  property :first_name
  property :last_name

user_data = {
  first_name: 'Freddy',
  last_name: 'Nostrils',
  email: '[email protected]'

p = Person.new(user_data) # 'email' is silently ignored

p.first_name # => 'Freddy'
p.last_name  # => 'Nostrils'
p.email      # => NoMethodError


This extension allows you to easily include a recursive merging system into any Hash descendant:

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

h1 = MyHash[{ x: { y: [4,5,6] }, z: [7,8,9] }]
h2 = MyHash[{ x: { y: [7,8,9] }, z: "xyz" }]

h1.deep_merge(h2) # => { x: { y: [7, 8, 9] }, z: "xyz" }
h2.deep_merge(h1) # => { x: { y: [4, 5, 6] }, z: [7, 8, 9] }

Like with Hash#merge in the standard library, a block can be provided to merge values:

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

h1 = MyHash[{ a: 100, b: 200, c: { c1: 100 } }]
h2 = MyHash[{ b: 250, c: { c1: 200 } }]

h1.deep_merge(h2) { |key, this_val, other_val| this_val + other_val }
# => { a: 100, b: 450, c: { c1: 300 } }


This extension can be mixed in to provide for safe and concise retrieval of deeply nested hash values. In the event that the requested key does not exist a block can be provided and its value will be returned.

Though this is a hash extension, it conveniently allows for arrays to be present in the nested structure. This feature makes the extension particularly useful for working with JSON API responses.

user = {
  name: { first: 'Bob', last: 'Boberts' },
  groups: [
    { name: 'Rubyists' },
    { name: 'Open source enthusiasts' }

user.extend Hashie::Extensions::DeepFetch

user.deep_fetch :name, :first # => 'Bob'
user.deep_fetch :name, :middle # => 'KeyError: Could not fetch middle'

# using a default block
user.deep_fetch(:name, :middle) { |key| 'default' }  # =>  'default'

# a nested array
user.deep_fetch :groups, 1, :name # => 'Open source enthusiasts'


This extension can be mixed in to provide for concise searching for keys within a deeply nested hash.

It can also search through any Enumerable contained within the hash for objects with the specified key.

Note: The searches are depth-first, so it is not guaranteed that a shallowly nested value will be found before a deeply nested value.

user = {
  name: { first: 'Bob', last: 'Boberts' },
  groups: [
    { name: 'Rubyists' },
    { name: 'Open source enthusiasts' }

user.extend Hashie::Extensions::DeepFind

user.deep_find(:name)   #=> { first: 'Bob', last: 'Boberts' }
user.deep_detect(:name) #=> { first: 'Bob', last: 'Boberts' }

user.deep_find_all(:name) #=> [{ first: 'Bob', last: 'Boberts' }, 'Rubyists', 'Open source enthusiasts']
user.deep_select(:name)   #=> [{ first: 'Bob', last: 'Boberts' }, 'Rubyists', 'Open source enthusiasts']


This extension can be mixed in to provide a depth first search based search for enumerables matching a given comparator callable.

It returns all enumerables which contain at least one element, for which the given comparator returns true.

Because the container objects are returned, the result elements can be modified in place. This way, one can perform modifications on deeply nested hashes without the need to know the exact paths.

books = [
    title: "Ruby for beginners",
    pages: 120
    title: "CSS for intermediates",
    pages: 80
    title: "Collection of ruby books",
    books: [
        title: "Ruby for the rest of us",
        pages: 576


# for ruby 1.9 leave *no* space between the lambda rocket and the braces
# http://ruby-journal.com/becareful-with-space-in-lambda-hash-rocket-syntax-between-ruby-1-dot-9-and-2-dot-0/

books.deep_locate -> (key, value, object) { key == :title && value.include?("Ruby") }
# => [{:title=>"Ruby for beginners", :pages=>120}, {:title=>"Ruby for the rest of us", :pages=>576}]

books.deep_locate -> (key, value, object) { key == :pages && value <= 120 }
# => [{:title=>"Ruby for beginners", :pages=>120}, {:title=>"CSS for intermediates", :pages=>80}]


This extension can be mixed in to allow a Hash to raise an error when attempting to extract a value using a non-existent key.

class StrictKeyAccessHash < Hash
  include Hashie::Extensions::StrictKeyAccess

>> hash = StrictKeyAccessHash[foo: "bar"]
=> {:foo=>"bar"}
>> hash[:foo]
=> "bar"
>> hash[:cow]
  KeyError: key not found: :cow


Mash is an extended Hash that gives simple pseudo-object functionality that can be built from hashes and easily extended. It is intended to give the user easier access to the objects within the Mash through a property-like syntax, while still retaining all Hash functionality.

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

mash = Hashie::Mash.new
# use under-bang methods for multi-level testing
mash.author_.name? # => false
mash.inspect # => <Hashie::Mash>

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.

How does Mash handle conflicts with pre-existing methods?

Please note that a Mash will not override methods through the use of the property-like syntax. This can lead to confusion if you expect to be able to access a Mash value through the property-like syntax for a key that conflicts with a method name. However, it protects users of your library from the unexpected behavior of those methods being overridden behind the scenes.

mash = Hashie::Mash.new
mash.name = "My Mash"
mash.zip = "Method Override?"
mash.zip # => [[["name", "My Mash"]], [["zip", "Method Override?"]]]

Since Mash gives you the ability to set arbitrary keys that then act as methods, Hashie logs when there is a conflict between a key and a pre-existing method. You can set the logger that this logs message to via the global Hashie logger:

Hashie.logger = Rails.logger

You can also disable the logging in subclasses of Mash:

class Response < Hashie::Mash

The default is to disable logging for all methods that conflict. If you would like to only disable the logging for specific methods, you can include an array of method keys:

class Response < Hashie::Mash
  disable_warnings :zip, :zap

This behavior is cumulative. The examples above and below behave identically.

class Response < Hashie::Mash
  disable_warnings :zip
  disable_warnings :zap

Disable warnings will honor the last disable_warnings call. Calling without parameters will override the ignored methods list, and calling with parameters will create a new ignored methods list. This includes child classes that inherit from a class that disables warnings.

class Message < Hashie::Mash
  disable_warnings :zip, :zap

# No errors will be logged
Message.new(merge: 'true', compact: true)
class Message < Hashie::Mash

class Response < Message
  disable_warnings :zip, :zap

# 2 errors will be logged
Response.new(merge: 'true', compact: true, zip: '90210', zap: 'electric')

If you would like to create an anonymous subclass of a Hashie::Mash with key conflict warnings disabled:

Hashie::Mash.quiet.new(zip: '90210', compact: true) # no errors logged
Hashie::Mash.quiet(:zip).new(zip: '90210', compact: true) # error logged for compact

How does the wrapping of Mash sub-Hashes work?

Mash duplicates any sub-Hashes that you add to it and wraps them in a Mash. This allows for infinite chaining of nested Hashes within a Mash without modifying the object(s) that are passed into the Mash. When you subclass Mash, the subclass wraps any sub-Hashes in its own class. This preserves any extensions that you mixed into the Mash subclass and allows them to work within the sub-Hashes, in addition to the main containing Mash.

mash = Hashie::Mash.new(name: "Hashie", dependencies: { rake: "< 11", rspec: "~> 3.0" })
mash.dependencies.class #=> Hashie::Mash

class MyGem < Hashie::Mash; end
my_gem = MyGem.new(name: "Hashie", dependencies: { rake: "< 11", rspec: "~> 3.0" })
my_gem.dependencies.class #=> MyGem

How does Mash handle key types which cannot be symbolized?

Mash preserves keys which cannot be converted directly to both a string and a symbol, such as numeric keys. Since Mash is conceived to provide psuedo-object functionality, handling keys which cannot represent a method call falls outside its scope of value.

Hashie::Mash.new('1' => 'one string', :'1' => 'one sym', 1 => 'one num')
# => {"1"=>"one sym", 1=>"one num"}

The symbol key :'1' is converted the string '1' to support indifferent access and consequently its value 'one sym' will override the previously set 'one string'. However, the subsequent key of 1 cannot directly convert to a symbol and therefore not converted to the string '1' that would otherwise override the previously set value of 'one sym'.

What else can Mash do?

Mash allows you also to transform any files into a Mash objects.

  api_key: 'api_key'
  api_key: <%= ENV['API_KEY'] %> #let's say that ENV['API_KEY'] is set to 'abcd'
mash = Mash.load('settings/twitter.yml')
mash.development.api_key # => 'localhost'
mash.development.api_key = "foo" # => <# RuntimeError can't modify frozen ...>
mash.development.api_key? # => true

You can also load with a Pathname object:

mash = Mash.load(Pathname 'settings/twitter.yml')
mash.development.api_key # => 'localhost'

You can access a Mash from another class:

mash = Mash.load('settings/twitter.yml')[ENV['RACK_ENV']]
Twitter.extend mash.to_module # NOTE: if you want another name than settings, call: to_module('my_settings')
Twitter.settings.api_key # => 'abcd'

You can use another parser (by default: YamlErbParser):

id | name          | lastname
---|------------- | -------------
1  |John          | Doe
2  |Laurent       | Garnier
mash = Mash.load('data/user.csv', parser: MyCustomCsvParser)
# => { 1 => { name: 'John', lastname: 'Doe'}, 2 => { name: 'Laurent', lastname: 'Garnier' } }
mash[1] #=> { name: 'John', lastname: 'Doe' }

The Mash#load method calls YAML.safe_load(path, [], [], true).

Specify permitted_symbols, permitted_classes and aliases options as needed.

Mash.load('data/user.csv', permitted_classes: [Symbol], permitted_symbols: [], aliases: false)


This extension can be mixed into a Mash to keep the form of any keys passed directly into the Mash. By default, Mash converts symbol keys to strings to give indifferent access. This extension still allows indifferent access, but keeps the form of the keys to eliminate confusion when you're not expecting the keys to change.

class KeepingMash < ::Hashie::Mash
  include Hashie::Extensions::Mash::KeepOriginalKeys

mash = KeepingMash.new(:symbol_key => :symbol, 'string_key' => 'string')
mash.to_hash == { :symbol_key => :symbol, 'string_key' => 'string' }  #=> true
mash.symbol_key  #=> :symbol
mash[:symbol_key]  #=> :symbol
mash['symbol_key']  #=> :symbol
mash.string_key  #=> 'string'
mash['string_key']  #=> 'string'
mash[:string_key]  #=> 'string'


By default, Mash only states that it responds to built-in methods, affixed methods (e.g. setters, underbangs, etc.), and keys that it currently contains. That means it won't state that it responds to a getter for an unset key, as in the following example:

mash = Hashie::Mash.new(a: 1)
mash.respond_to? :b  #=> false

This means that by default Mash is not a perfect match for use with a SimpleDelegator since the delegator will not forward messages for unset keys to the Mash even though it can handle them.

In order to have a SimpleDelegator-compatible Mash, you can use the PermissiveRespondTo extension to make Mash respond to anything.

class PermissiveMash < Hashie::Mash
  include Hashie::Extensions::Mash::PermissiveRespondTo

mash = PermissiveMash.new(a: 1)
mash.respond_to? :b  #=> true

This comes at the cost of approximately 20% performance for initialization and setters and 19KB of permanent memory growth for each such class that you create.


This extension can be mixed into a Mash to guard the attempted overwriting of methods by property setters. When mixed in, the Mash will raise an ArgumentError if you attempt to write a property with the same name as an existing method.

class SafeMash < ::Hashie::Mash
  include Hashie::Extensions::Mash::SafeAssignment

safe_mash = SafeMash.new
safe_mash.zip   = 'Test' # => ArgumentError
safe_mash[:zip] = 'test' # => still ArgumentError


This extension can be mixed into a Mash to change the default behavior of converting keys to strings. After mixing this extension into a Mash, the Mash will convert all string keys to symbols. It can be useful to use with keywords argument, which required symbol keys.

class SymbolizedMash < ::Hashie::Mash
  include Hashie::Extensions::Mash::SymbolizeKeys

symbol_mash = SymbolizedMash.new
symbol_mash['test'] = 'value'
symbol_mash.test  #=> 'value'
symbol_mash.to_h  #=> {test: 'value'}

def example(test:)
  puts test

example(symbol_mash) #=> value

There is a major benefit and coupled with a major trade-off to this decision (at least on older Rubies). As a benefit, by using symbols as keys, you will be able to use the implicit conversion of a Mash via the #to_hash method to destructure (or splat) the contents of a Mash out to a block. This can be handy for doing iterations through the Mash's keys and values, as follows:

symbol_mash = SymbolizedMash.new(id: 123, name: 'Rey')
symbol_mash.each do |key, value|
  # key is :id, then :name
  # value is 123, then 'Rey'

However, on Rubies less than 2.0, this means that every key you send to the Mash will generate a symbol. Since symbols are not garbage-collected on older versions of Ruby, this can cause a slow memory leak when using a symbolized Mash with data generated from user input.


This extension can be mixed into a Mash so it makes it behave like OpenStruct. It reduces the overhead of method_missing? magic by lazily defining field accessors when they're requested.

class MyHash < ::Hashie::Mash
  include Hashie::Extensions::Mash::DefineAccessors

mash = MyHash.new
MyHash.method_defined?(:foo=) #=> false
mash.foo = 123
MyHash.method_defined?(:foo=) #=> true

MyHash.method_defined?(:foo) #=> false
mash.foo #=> 123
MyHash.method_defined?(:foo) #=> true

You can also extend the existing mash without defining a class:

mash = ::Hashie::Mash.new.with_accessors!


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 exception if unset. Another option is message for required properties, which allow you to add custom messages for required property.

You can also conditionally require certain properties by passing a Proc or Symbol. If a Proc is provided, it will be run in the context of the Dash instance. If a Symbol is provided, the value returned for the property or method of the same name will be evaluated. The property will be required if the result of the conditional is truthy.

class Person < Hashie::Dash
  property :name, required: true
  property :age, required: true, message: 'must be set.'
  property :email
  property :phone, required: -> { email.nil? }, message: 'is required if email is not set.'
  property :pants, required: :weekday?, message: 'are only required on weekdays.'
  property :occupation, default: 'Rubyist'

  def weekday?
    [ Time.now.saturday?, Time.now.sunday? ].none?

p = Person.new # => ArgumentError: The property 'name' is required for this Dash.
p = Person.new(name: 'Bob') # => ArgumentError: The property 'age' must be set.

p = Person.new(name: "Bob", age: 18)
p.name         # => 'Bob'
p.name = nil   # => ArgumentError: The property 'name' is required for this Dash.
p.age          # => 18
p.age = nil    # => ArgumentError: The property 'age' must be set.
p.email = '[email protected]'
p.occupation   # => 'Rubyist'
p.email        # => '[email protected]'
p[:awesome]    # => NoMethodError
p[:occupation] # => 'Rubyist'
p.update_attributes!(name: 'Trudy', occupation: 'Evil')
p.occupation   # => 'Evil'
p.name         # => 'Trudy'
p.update_attributes!(occupation: nil)
p.occupation   # => 'Rubyist'

Properties defined as symbols are not the same thing as properties defined as strings.

class Tricky < Hashie::Dash
  property :trick
  property 'trick'

p = Tricky.new(trick: 'one', 'trick' => 'two')
p.trick # => 'one', always symbol version
p[:trick] # => 'one'
p['trick'] # => 'two'

Note that accessing a property as a method always uses the symbol version.

class Tricky < Hashie::Dash
  property 'trick'

p = Tricky.new('trick' => 'two')
p.trick # => NoMethodError

If you would like to update a Dash and use any default values set in the case of a nil value, use #update_attributes!.

class WithDefaults < Hashie::Dash
  property :description, default: 'none'

dash = WithDefaults.new
dash.description  #=> 'none'

dash.description = 'You committed one of the classic blunders!'
dash.description  #=> 'You committed one of the classic blunders!'

dash.description = nil
dash.description  #=> nil

dash.description = 'Only slightly less known is ...'
dash.update_attributes!(description: nil)
dash.description  #=> 'none'

Potential Gotchas

Because Dashes are subclasses of the built-in Ruby Hash class, the double-splat operator takes the Dash as-is without any conversion. This can lead to strange behavior when you use the double-splat operator on a Dash as the first part of a keyword list or built Hash. For example:

class Foo < Hashie::Dash
  property :bar

foo = Foo.new(bar: 'baz')      #=> {:bar=>"baz"}
qux = { **foo, quux: 'corge' } #=> {:bar=> "baz", :quux=>"corge"}
qux.is_a?(Foo)                 #=> true
#=> raise NoMethodError, "The property 'quux' is not defined for Foo."
qux.key?(:quux) #=> true

You can work around this problem in two ways:

  1. Call #to_h on the resulting object to convert it into a Hash.
  2. Use the double-splat operator on the Dash as the last argument in the Hash literal. This will cause the resulting object to be a Hash instead of a Dash, thereby circumventing the problem.
qux = { **foo, quux: 'corge' }.to_h #=> {:bar=> "baz", :quux=>"corge"}
qux.is_a?(Hash)                     #=> true
qux[:quux]                          #=> "corge"

qux = { quux: 'corge', **foo } #=> {:quux=>"corge", :bar=> "baz"}
qux.is_a?(Hash)                #=> true
qux[:quux]                     #=> "corge"


The Hashie::Extensions::Dash::PropertyTranslation mixin extends a Dash with the ability to remap keys from a source hash.

Property translation is useful when you need to read data from another application -- such as a Java API -- where the keys are named differently from Ruby conventions.

class PersonHash < Hashie::Dash
  include Hashie::Extensions::Dash::PropertyTranslation

  property :first_name, from: :firstName
  property :last_name, from: :lastName
  property :first_name, from: :f_name
  property :last_name, from: :l_name

person = PersonHash.new(firstName: 'Michael', l_name: 'Bleigh')
person[:first_name]  #=> 'Michael'
person[:last_name]   #=> 'Bleigh

You can also use a lambda to translate the value. This is particularly useful when you want to ensure the type of data you're wrapping.

class DataModelHash < Hashie::Dash
  include Hashie::Extensions::Dash::PropertyTranslation

  property :id, transform_with: ->(value) { value.to_i }
  property :created_at, from: :created, with: ->(value) { Time.parse(value) }

model = DataModelHash.new(id: '123', created: '2014-04-25 22:35:28')
model.id.class          #=> Integer (Fixnum if you are using Ruby 2.3 or lower)
model.created_at.class  #=> Time

Mash and Rails 4 Strong Parameters

To enable compatibility with Rails 4 use the hashie-forbidden_attributes gem.


If you want to use Hashie::Extensions::Coercion together with Dash then you may probably want to use Hashie::Extensions::Dash::Coercion instead. This extension automatically includes Hashie::Extensions::Coercion and also adds a convenient :coerce option to property so you can define coercion in one line instead of using property and coerce_key separate:

class UserHash < Hashie::Dash
  include Hashie::Extensions::Coercion

  property :id
  property :posts

  coerce_key :posts, Array[PostHash]

This is the same as:

class UserHash < Hashie::Dash
  include Hashie::Extensions::Dash::Coercion

  property :id
  property :posts, coerce: Array[PostHash]


The Hashie::Extensions::Dash::PredefinedValues mixin extends a Dash with the ability to accept predefined values on a property.

class UserHash < Hashie::Dash
  include Hashie::Extensions::Dash::PredefinedValues

  property :gender, values: %i[male female prefer_not_to_say]
  property :age, values: (0..150)


A Trash is a Dash that allows you to translate keys on initialization. It mixes in the PropertyTranslation mixin by default and 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')

Trash also supports translations using lambda, this could be useful when dealing with external API's. You can use it in this way:

class Result < Hashie::Trash
  property :id, transform_with: lambda { |v| v.to_i }
  property :created_at, from: :creation_date, with: lambda { |v| Time.parse(v) }

this will produce the following

result = Result.new(id: '123', creation_date: '2012-03-30 17:23:28')
result.id.class         # => Integer (Fixnum if you are using Ruby 2.3 or lower)
result.created_at.class # => Time


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 } }


Rash is a Hash whose keys can be Regexps or Ranges, which will map many input keys to a value.

A good use case for the Rash is an URL router for a web framework, where URLs need to be mapped to actions; the Rash's keys match URL patterns, while the values call the action which handles the URL.

If the Rash's value is a proc, the proc will be automatically called with the regexp's MatchData (matched groups) as a block argument.

# Mapping names to appropriate greetings
greeting = Hashie::Rash.new( /^Mr./ => "Hello sir!", /^Mrs./ => "Evening, madame." )
greeting["Mr. Steve Austin"] # => "Hello sir!"
greeting["Mrs. Steve Austin"] # => "Evening, madame."

# Mapping statements to saucy retorts
mapper = Hashie::Rash.new(
  /I like (.+)/ => proc { |m| "Who DOESN'T like #{m[1]}?!" },
  /Get off my (.+)!/ => proc { |m| "Forget your #{m[1]}, old man!" }
mapper["I like traffic lights"] # => "Who DOESN'T like traffic lights?!"
mapper["Get off my lawn!"]      # => "Forget your lawn, old man!"


Note: The Rash is automatically optimized every 500 accesses (which means that it sorts the list of Regexps, putting the most frequently matched ones at the beginning).

If this value is too low or too high for your needs, you can tune it by setting: rash.optimize_every = n.


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Copyright (c) 2009-2020 Intridea, Inc., and contributors.

MIT License. See LICENSE for details.