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.

Examples:

require 'ostruct'

person = OpenStruct.new
person.name    = "John Smith"
person.age     = 70
person.pension = 300

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

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

australia = OpenStruct.new(:country => "Australia", :population => 20_000_000)
p australia   # -> <OpenStruct country="Australia" population=20000000>

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

measurements = OpenStruct.new("length (in inches)" => 24)
measurements.send("length (in inches)")  # -> 24

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

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

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

first_pet == second_pet   # -> false

first_pet.delete_field(:owner)
first_pet == second_pet   # -> true

Implementation:

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

Methods
A
J
T
Class Public methods
json_create(object)

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

# File ext/json/lib/json/add/ostruct.rb, line 11
def self.json_create(object)
  new(object['t'] || object[:t])
end
Instance Public methods
as_json(*)

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

# 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,
  }
end
to_json(*args)

Stores class name (OpenStruct) with this struct's values v as a JSON string.

# File ext/json/lib/json/add/ostruct.rb, line 28
def to_json(*args)
  as_json.to_json(*args)
end