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Showing content from https://docs.ruby-lang.org/en/3.4/OpenStruct.html below:

class OpenStruct - Documentation for Ruby 3.4

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.

require "ostruct"

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

person.name      
person.age       
person.address   

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")
  

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)"]       
measurements.send("length (in inches)")   

message = OpenStruct.new(:queued? => true)
message.queued?                           
message.send("queued?=", false)
message.queued?                           

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                 
first_pet == second_pet   

first_pet.delete_field(:owner)
first_pet                 
first_pet == second_pet   

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

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 

Builtin methods may be overwritten this way, which may be a source of bugs or security issues:

o = OpenStruct.new
o.methods 
o.methods = [:foo, :bar]
o.methods 

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 
o.class! 

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.

HAS_PERFORMANCE_WARNINGS

VERSION

def self.json_create(object)
  new(object['t'] || object[:t])
end

See as_json.

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   

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   
first_pet == third_pet    

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]   

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   
person.age          

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

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

OpenStruct.json_create(x)

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")  
person                       

Setting the value to nil will not remove the attribute:

person.pension = nil
person                 

person.delete_field('number')  

person.delete_field('number') { 8675_309 } 

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") 
person.dig(:business_address, "zip") 

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   

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?.

def freeze
  @table.freeze
  super
end

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.

def to_h(&block)
  if block
    @table.to_h(&block)
  else
    @table.dup
  end
end

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}}

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