/Ruby 3

class OpenStruct


An OpenStruct is a data structure, similar to a Hash, that allows the definition of arbitrary attributes with their accompanying values. This is accomplished by using Ruby's metaprogramming to define methods on the class itself.


require "ostruct"

person = OpenStruct.new
person.name = "John Smith"
person.age  = 70

person.name      # => "John Smith"
person.age       # => 70
person.address   # => nil

An OpenStruct employs a Hash internally to store the attributes and values and can even be initialized with one:

australia = OpenStruct.new(:country => "Australia", :capital => "Canberra")
  # => #<OpenStruct country="Australia", capital="Canberra">

Hash keys with spaces or characters that could normally not be used for method calls (e.g. ()[]*) will not be immediately available on the OpenStruct object as a method for retrieval or assignment, but can still be reached through the Object#send method or using [].

measurements = OpenStruct.new("length (in inches)" => 24)
measurements[:"length (in inches)"]       # => 24
measurements.send("length (in inches)")   # => 24

message = OpenStruct.new(:queued? => true)
message.queued?                           # => true
message.send("queued?=", false)
message.queued?                           # => false

Removing the presence of an attribute requires the execution of the delete_field method as setting the property value to nil will not remove the attribute.

first_pet  = OpenStruct.new(:name => "Rowdy", :owner => "John Smith")
second_pet = OpenStruct.new(:name => "Rowdy")

first_pet.owner = nil
first_pet                 # => #<OpenStruct name="Rowdy", owner=nil>
first_pet == second_pet   # => false

first_pet                 # => #<OpenStruct name="Rowdy">
first_pet == second_pet   # => true

Ractor compatibility: A frozen OpenStruct with shareable values is itself shareable.


An OpenStruct utilizes Ruby's method lookup structure to find and define the necessary methods for properties. This is accomplished through the methods method_missing and define_singleton_method.

This should be a consideration if there is a concern about the performance of the objects that are created, as there is much more overhead in the setting of these properties compared to using a Hash or a Struct. Creating an open struct from a small Hash and accessing a few of the entries can be 200 times slower than accessing the hash directly.

This is a potential security issue; building OpenStruct from untrusted user data (e.g. JSON web request) may be susceptible to a “symbol denial of service” attack since the keys create methods and names of methods are never garbage collected.

This may also be the source of incompatibilities between Ruby versions:

o = OpenStruct.new
o.then # => nil in Ruby < 2.6, enumerator for Ruby >= 2.6

Builtin methods may be overwritten this way, which may be a source of bugs or security issues:

o = OpenStruct.new
o.methods # => [:to_h, :marshal_load, :marshal_dump, :each_pair, ...
o.methods = [:foo, :bar]
o.methods # => [:foo, :bar]

To help remedy clashes, OpenStruct uses only protected/private methods ending with `!` and defines aliases for builtin public methods by adding a `!`:

o = OpenStruct.new(make: 'Bentley', class: :luxury)
o.class # => :luxury
o.class! # => OpenStruct

It is recommended (but not enforced) to not use fields ending in `!`; Note that a subclass' methods may not be overwritten, nor can OpenStruct's own methods ending with `!`.

For all these reasons, consider not using OpenStruct at all.



Public Class Methods

json_create(object) Show source
# File ext/json/lib/json/add/ostruct.rb, line 11
def self.json_create(object)
  new(object['t'] || object[:t])

Deserializes JSON string by constructing new Struct object with values t serialized by to_json.

new(hash=nil) Show source
# File lib/ostruct.rb, line 126
def initialize(hash=nil)
  if hash
    @table = {}

Creates a new OpenStruct object. By default, the resulting OpenStruct object will have no attributes.

The optional hash, if given, will generate attributes and values (can be a Hash, an OpenStruct or a Struct). For example:

require "ostruct"
hash = { "country" => "Australia", :capital => "Canberra" }
data = OpenStruct.new(hash)

data   # => #<OpenStruct country="Australia", capital="Canberra">

Public Instance Methods

==(other) Show source
# File lib/ostruct.rb, line 376
def ==(other)
  return false unless other.kind_of?(OpenStruct)
  @table == other.table!

Compares this object and other for equality. An OpenStruct is equal to other when other is an OpenStruct and the two objects' Hash tables are equal.

require "ostruct"
first_pet  = OpenStruct.new("name" => "Rowdy")
second_pet = OpenStruct.new(:name  => "Rowdy")
third_pet  = OpenStruct.new("name" => "Rowdy", :age => nil)

first_pet == second_pet   # => true
first_pet == third_pet    # => false
ostruct[name] → object Show source
# File lib/ostruct.rb, line 263
def [](name)

Returns the value of an attribute, or `nil` if there is no such attribute.

require "ostruct"
person = OpenStruct.new("name" => "John Smith", "age" => 70)
person[:age]   # => 70, same as person.age
ostruct[name] = obj → obj Show source
# File lib/ostruct.rb, line 278
def []=(name, value)
  name = name.to_sym
  @table[name] = value

Sets the value of an attribute.

require "ostruct"
person = OpenStruct.new("name" => "John Smith", "age" => 70)
person[:age] = 42   # equivalent to person.age = 42
person.age          # => 42
Also aliased as: set_ostruct_member_value!
as_json(*) Show source
# File ext/json/lib/json/add/ostruct.rb, line 17
def as_json(*)
  klass = self.class.name
  klass.to_s.empty? and raise JSON::JSONError, "Only named structs are supported!"
    JSON.create_id => klass,
    't'            => table,

Returns a hash, that will be turned into a JSON object and represent this object.

delete_field(name) Show source
# File lib/ostruct.rb, line 325
def delete_field(name)
  sym = name.to_sym
    singleton_class.remove_method(sym, "#{sym}=")
  rescue NameError
  @table.delete(sym) do
    raise! NameError.new("no field `#{sym}' in #{self}", sym)

Removes the named field from the object. Returns the value that the field contained if it was defined.

require "ostruct"

person = OpenStruct.new(name: "John", age: 70, pension: 300)

person.delete_field!("age")  # => 70
person                       # => #<OpenStruct name="John", pension=300>

Setting the value to nil will not remove the attribute:

person.pension = nil
person                 # => #<OpenStruct name="John", pension=nil>
dig(name, *identifiers) → object Show source
# File lib/ostruct.rb, line 300
def dig(name, *names)
    name = name.to_sym
  rescue NoMethodError
    raise! TypeError, "#{name} is not a symbol nor a string"
  @table.dig(name, *names)

Finds and returns the object in nested objects that is specified by name and identifiers. The nested objects may be instances of various classes. See Dig Methods.


require "ostruct"
address = OpenStruct.new("city" => "Anytown NC", "zip" => 12345)
person  = OpenStruct.new("name" => "John Smith", "address" => address)
person.dig(:address, "zip") # => 12345
person.dig(:business_address, "zip") # => nil
each_pair {|name, value| block } → ostruct Show source
each_pair → Enumerator
# File lib/ostruct.rb, line 189
def each_pair
  return to_enum(__method__) { @table.size } unless block_given?
  @table.each_pair{|p| yield p}

Yields all attributes (as symbols) along with the corresponding values or returns an enumerator if no block is given.

require "ostruct"
data = OpenStruct.new("country" => "Australia", :capital => "Canberra")
data.each_pair.to_a   # => [[:country, "Australia"], [:capital, "Canberra"]]
eql?(other) Show source
# File lib/ostruct.rb, line 386
def eql?(other)
  return false unless other.kind_of?(OpenStruct)

Compares this object and other for equality. An OpenStruct is eql? to other when other is an OpenStruct and the two objects' Hash tables are eql?.

freeze() Show source
# File lib/ostruct.rb, line 230
def freeze
Calls superclass method Object#freeze
inspect() Show source
# File lib/ostruct.rb, line 341
def inspect
  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    detail = ' ...'
    ids << object_id
      detail = @table.map do |key, value|
        " #{key}=#{value.inspect}"
  ['#<', self.class!, detail, '>'].join

Returns a string containing a detailed summary of the keys and values.

Also aliased as: to_s
to_h → hash Show source
to_h {|name, value| block } → hash
# File lib/ostruct.rb, line 169
def to_h(&block)
  if block

Converts the OpenStruct to a hash with keys representing each attribute (as symbols) and their corresponding values.

If a block is given, the results of the block on each pair of the receiver will be used as pairs.

require "ostruct"
data = OpenStruct.new("country" => "Australia", :capital => "Canberra")
data.to_h   # => {:country => "Australia", :capital => "Canberra" }
data.to_h {|name, value| [name.to_s, value.upcase] }
            # => {"country" => "AUSTRALIA", "capital" => "CANBERRA" }
to_json(*args) Show source
# File ext/json/lib/json/add/ostruct.rb, line 28
def to_json(*args)

Stores class name (OpenStruct) with this struct's values t as a JSON string.

Alias for: inspect

Private Instance Methods

Alias for: []=

Ruby Core © 1993–2020 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.