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
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Constants
InspectKey = :__inspect_key__
 
Class Public methods
json_create(object)

Deserializes JSON string by constructing new Struct object with values t 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
new(hash=nil)

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", :population => 20_000_000 }
data = OpenStruct.new(hash)

p data        # -> <OpenStruct country="Australia" population=20000000>
# File lib/ostruct.rb, line 89
def initialize(hash=nil)
  @table = {}
  if hash
    hash.each_pair do |k, v|
      k = k.to_sym
      @table[k] = v
    end
  end
end
Instance Public methods
==(other)

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.

# File lib/ostruct.rb, line 309
def ==(other)
  return false unless other.kind_of?(OpenStruct)
  @table == other.table!
end
[](name)

Returns the value of a member.

person = OpenStruct.new('name' => 'John Smith', 'age' => 70)
person[:age] # => 70, same as ostruct.age
# File lib/ostruct.rb, line 218
def [](name)
  @table[name.to_sym]
end
[]=(name, value)

Sets the value of a member.

person = OpenStruct.new('name' => 'John Smith', 'age' => 70)
person[:age] = 42 # => equivalent to ostruct.age = 42
person.age # => 42
# File lib/ostruct.rb, line 229
def []=(name, value)
  modifiable?[new_ostruct_member!(name)] = value
end
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
delete_field(name)

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

require 'ostruct'

person = OpenStruct.new('name' => 'John Smith', 'age' => 70)

person.delete_field('name')  # => 'John Smith'
# File lib/ostruct.rb, line 261
def delete_field(name)
  sym = name.to_sym
  begin
    singleton_class.__send__(:remove_method, sym, "#{sym}=")
  rescue NameError
  end
  @table.delete(sym) do
    raise NameError.new("no field `#{sym}' in #{self}", sym)
  end
end
dig(name, *names)

Retrieves the value object corresponding to the each name objects repeatedly.

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
# File lib/ostruct.rb, line 242
def dig(name, *names)
  begin
    name = name.to_sym
  rescue NoMethodError
    raise TypeError, "#{name} is not a symbol nor a string"
  end
  @table.dig(name, *names)
end
each_pair()

Yields all attributes (as a symbol) along with the corresponding values or returns an enumerator if not block is given. Example:

require 'ostruct'
data = OpenStruct.new("country" => "Australia", :population => 20_000_000)
data.each_pair.to_a  # => [[:country, "Australia"], [:population, 20000000]]
# File lib/ostruct.rb, line 127
def each_pair
  return to_enum(__method__) { @table.size } unless block_given?
  @table.each_pair{|p| yield p}
  self
end
eql?(other)

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?.

# File lib/ostruct.rb, line 319
def eql?(other)
  return false unless other.kind_of?(OpenStruct)
  @table.eql?(other.table!)
end
freeze()
# File lib/ostruct.rb, line 184
def freeze
  @table.each_key {|key| new_ostruct_member!(key)}
  super
end
hash()

Compute a hash-code for this OpenStruct. Two hashes with the same content will have the same hash code (and will be eql?).

# File lib/ostruct.rb, line 327
def hash
  @table.hash
end
initialize_copy(orig)

Duplicate an OpenStruct object members.

# File lib/ostruct.rb, line 100
def initialize_copy(orig)
  super
  @table = @table.dup
end
inspect()

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

Also aliased as: to_s
# File lib/ostruct.rb, line 277
def inspect
  str = "#<#{self.class}"

  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    return str << ' ...>'
  end

  ids << object_id
  begin
    first = true
    for k,v in @table
      str << "," unless first
      first = false
      str << " #{k}=#{v.inspect}"
    end
    return str << '>'
  ensure
    ids.pop
  end
end
marshal_dump()

Provides marshalling support for use by the Marshal library.

# File lib/ostruct.rb, line 136
def marshal_dump
  @table
end
marshal_load(x)

Provides marshalling support for use by the Marshal library.

# File lib/ostruct.rb, line 143
def marshal_load(x)
  @table = x
end
respond_to_missing?(mid, include_private = false)
# File lib/ostruct.rb, line 189
def respond_to_missing?(mid, include_private = false)
  mname = mid.to_s.chomp("=").to_sym
  @table&.key?(mname) || super
end
to_h()

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

require 'ostruct'
data = OpenStruct.new("country" => "Australia", :population => 20_000_000)
data.to_h   # => {:country => "Australia", :population => 20000000 }
# File lib/ostruct.rb, line 114
def to_h
  @table.dup
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
to_s()
Alias for: inspect