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

VERSION

Public Class Methods

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 ostruct.rb, line 126
def initialize(hash=nil)
  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 ostruct.rb, line 376
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 ostruct.rb, line 263
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 ostruct.rb, line 278
def []=(name, value)
  name = name.to_sym
  new_ostruct_member!(name)
  @table[name] = value
end

Also aliased as: set_ostruct_member_value!

delete_field(name) click to toggle source

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>

 
               # File ostruct.rb, line 325
def delete_field(name)
  sym = name.to_sym
  begin
    singleton_class.remove_method(sym, "#{sym}=")
  rescue NameError
  end
  @table.delete(sym) do
    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 ostruct.rb, line 300
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 ostruct.rb, line 189
def each_pair
  return to_enum(__method__) { @table.size } unless block_given?
  @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 ostruct.rb, line 386
def eql?(other)
  return false unless other.kind_of?(OpenStruct)
  @table.eql?(other.table!)
end

freeze() click to toggle source

 
               # File ostruct.rb, line 230
def freeze
  @table.freeze
  super
end

inspect() click to toggle source

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

 
               # File ostruct.rb, line 341
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 → hash click to toggle source

to_h {|name, value| block } → hash

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" }

 
               # File ostruct.rb, line 169
def to_h(&block)
  if block
    @table.to_h(&block)
  else
    @table.dup
  end
end

to_s() click to toggle source

Alias for: inspect

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