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.

Examples¶ ↑

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.delete_field(:owner)
first_pet                 # => #<OpenStruct name="Rowdy">
first_pet == second_pet   # => true

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

Caveats¶ ↑

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.

Constants

HAS_PERFORMANCE_WARNINGS
VERSION

Public Class Methods

json_create(object) click to toggle source

See as_json.

# File ext/json/lib/json/add/ostruct.rb, line 13
def self.json_create(object)
  new(object['t'] || object[:t])
end

new(hash=nil) click to toggle source

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">

# File lib/ostruct.rb, line 134
def initialize(hash=nil)
  if HAS_PERFORMANCE_WARNINGS && Warning[:performance]
     warn "OpenStruct use is discouraged for performance reasons", uplevel: 1, category: :performance
  end

  if hash
    update_to_values!(hash)
  else
    @table = {}
  end
end

Public Instance Methods

==(other) click to toggle source

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

# File lib/ostruct.rb, line 423
def ==(other)
  return false unless other.kind_of?(OpenStruct)
  @table == other.table!
end

ostruct[name] → object click to toggle source

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

# File lib/ostruct.rb, line 303
def [](name)
  @table[name.to_sym]
end

ostruct[name] = obj → obj click to toggle source

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

# File lib/ostruct.rb, line 318
def []=(name, value)
  name = name.to_sym
  new_ostruct_member!(name)
  @table[name] = value
end

Also aliased as: set_ostruct_member_value!

as_json(*) click to toggle source

Methods OpenStruct#as_json and OpenStruct.json_create may be used to serialize and deserialize a OpenStruct object; see Marshal.

Method OpenStruct#as_json serializes self, returning a 2-element hash representing self:

require 'json/add/ostruct'
x = OpenStruct.new('name' => 'Rowdy', :age => nil).as_json
# => {"json_class"=>"OpenStruct", "t"=>{:name=>'Rowdy', :age=>nil}}

Method JSON.create deserializes such a hash, returning a OpenStruct object:

OpenStruct.json_create(x)
# => #<OpenStruct name='Rowdy', age=nil>

# File ext/json/lib/json/add/ostruct.rb, line 33
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) { || ... } click to toggle source

Removes the named field from the object and returns the value the field contained if it was defined. You may optionally provide a block. If the field is not defined, the result of the block is returned, or a NameError is raised if no block was given.

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>

person.delete_field('number')  # => NameError

person.delete_field('number') { 8675_309 } # => 8675309

# File lib/ostruct.rb, line 371
def delete_field(name, &block)
  sym = name.to_sym
  begin
    singleton_class.remove_method(sym, "#{sym}=")
  rescue NameError
  end
  @table.delete(sym) do
    return yield if block
    raise! NameError.new("no field `#{sym}' in #{self}", sym)
  end
end

dig(name, *identifiers) → object click to toggle source

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.

Examples:

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

# File lib/ostruct.rb, line 340
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 {|name, value| block } → ostruct click to toggle source

each_pair → Enumerator

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"]]

# File lib/ostruct.rb, line 211
def each_pair
  return to_enum(__method__) { @table.size } unless defined?(yield)
  @table.each_pair{|p| yield p}
  self
end

eql?(other) click to toggle source

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 433
def eql?(other)
  return false unless other.kind_of?(OpenStruct)
  @table.eql?(other.table!)
end

freeze() click to toggle source

Calls superclass method Object#freeze

# File lib/ostruct.rb, line 269
def freeze
  @table.freeze
  super
end

inspect() click to toggle source

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

# File lib/ostruct.rb, line 388
def inspect
  ids = (Thread.current[InspectKey] ||= [])
  if ids.include?(object_id)
    detail = ' ...'
  else
    ids << object_id
    begin
      detail = @table.map do |key, value|
        " #{key}=#{value.inspect}"
      end.join(',')
    ensure
      ids.pop
    end
  end
  ['#<', self.class!, detail, '>'].join
end

Also aliased as: to_s

to_h(&block) click to toggle source

# File lib/ostruct.rb, line 182
def to_h(&block)
  if block
    @table.to_h(&block)
  else
    @table.dup
  end
end

to_json(*args) click to toggle source

Returns a JSON string representing self:

require 'json/add/ostruct'
puts OpenStruct.new('name' => 'Rowdy', :age => nil).to_json

Output:

{"json_class":"OpenStruct","t":{'name':'Rowdy',"age":null}}

# File ext/json/lib/json/add/ostruct.rb, line 51
def to_json(*args)
  as_json.to_json(*args)
end

to_s()

Alias for: inspect

Private Instance Methods

set_ostruct_member_value!

Alias for: []=