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.
# File tmp/rubies/ruby-3.3.0/ext/json/lib/json/add/ostruct.rb, line 10
def self.json_create(object)
new(object['t'] || object[:t])
end
See as_json.
# File tmp/rubies/ruby-3.3.0/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
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 tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 423
def ==(other)
return false unless other.kind_of?(OpenStruct)
@table == other.table!
end
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 tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 303
def [](name)
@table[name.to_sym]
end
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 tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 318
def []=(name, value)
name = name.to_sym
new_ostruct_member!(name)
@table[name] = value
end
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 tmp/rubies/ruby-3.3.0/ext/json/lib/json/add/ostruct.rb, line 30
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
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 tmp/rubies/ruby-3.3.0/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
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 tmp/rubies/ruby-3.3.0/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
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 tmp/rubies/ruby-3.3.0/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
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 tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 433
def eql?(other)
return false unless other.kind_of?(OpenStruct)
@table.eql?(other.table!)
end
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 tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 269
def freeze
@table.freeze
super
end
# File tmp/rubies/ruby-3.3.0/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
Returns a string containing a detailed summary of the keys and values.
# File tmp/rubies/ruby-3.3.0/lib/ostruct.rb, line 182
def to_h(&block)
if block
@table.to_h(&block)
else
@table.dup
end
end
# File tmp/rubies/ruby-3.3.0/ext/json/lib/json/add/ostruct.rb, line 48
def to_json(*args)
as_json.to_json(*args)
end
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}}