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Filename : ostruct.rb
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# frozen_string_literal: false
#
# = ostruct.rb: OpenStruct implementation
#
# Author:: Yukihiro Matsumoto
# Documentation:: Gavin Sinclair
#
# OpenStruct allows the creation of data objects with arbitrary attributes.
# See OpenStruct for an example.
#

#
# 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. <code>()[]*</code>) 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.
#
#   measurements = OpenStruct.new("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
#
#
# == Implementation
#
# 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.
#
class OpenStruct

  #
  # 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">
  #
  def initialize(hash=nil)
    @table = {}
    if hash
      hash.each_pair do |k, v|
        k = k.to_sym
        @table[k] = v
      end
    end
  end

  # Duplicates an OpenStruct object's Hash table.
  def initialize_copy(orig) # :nodoc:
    super
    @table = @table.dup
  end

  #
  # Converts the OpenStruct to a hash with keys representing
  # each attribute (as symbols) and their corresponding values.
  #
  #   require "ostruct"
  #   data = OpenStruct.new("country" => "Australia", :capital => "Canberra")
  #   data.to_h   # => {:country => "Australia", :capital => "Canberra" }
  #
  def to_h
    @table.dup
  end

  #
  # :call-seq:
  #   ostruct.each_pair {|name, value| block }  -> ostruct
  #   ostruct.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"]]
  #
  def each_pair
    return to_enum(__method__) { @table.size } unless block_given?
    @table.each_pair{|p| yield p}
    self
  end

  #
  # Provides marshalling support for use by the Marshal library.
  #
  def marshal_dump
    @table
  end

  #
  # Provides marshalling support for use by the Marshal library.
  #
  def marshal_load(x)
    @table = x
  end

  #
  # Used internally to check if the OpenStruct is able to be
  # modified before granting access to the internal Hash table to be modified.
  #
  def modifiable? # :nodoc:
    begin
      @modifiable = true
    rescue
      raise RuntimeError, "can't modify frozen #{self.class}", caller(3)
    end
    @table
  end
  private :modifiable?

  # ::Kernel.warn("#{caller(1, 1)[0]}: do not use OpenStruct#modifiable")
  alias modifiable modifiable? # :nodoc:
  protected :modifiable

  #
  # Used internally to defined properties on the
  # OpenStruct. It does this by using the metaprogramming function
  # define_singleton_method for both the getter method and the setter method.
  #
  def new_ostruct_member!(name) # :nodoc:
    name = name.to_sym
    unless singleton_class.method_defined?(name)
      define_singleton_method(name) { @table[name] }
      define_singleton_method("#{name}=") {|x| modifiable?[name] = x}
    end
    name
  end
  private :new_ostruct_member!

  # ::Kernel.warn("#{caller(1, 1)[0]}: do not use OpenStruct#new_ostruct_member")
  alias new_ostruct_member new_ostruct_member! # :nodoc:
  protected :new_ostruct_member

  def freeze
    @table.each_key {|key| new_ostruct_member!(key)}
    super
  end

  def respond_to_missing?(mid, include_private = false) # :nodoc:
    mname = mid.to_s.chomp("=").to_sym
    @table&.key?(mname) || super
  end

  def method_missing(mid, *args) # :nodoc:
    len = args.length
    if mname = mid[/.*(?==\z)/m]
      if len != 1
        raise ArgumentError, "wrong number of arguments (#{len} for 1)", caller(1)
      end
      modifiable?[new_ostruct_member!(mname)] = args[0]
    elsif len == 0
      if @table.key?(mid)
        new_ostruct_member!(mid) unless frozen?
        @table[mid]
      end
    else
      err = NoMethodError.new "undefined method `#{mid}' for #{self}", mid, args
      err.set_backtrace caller(1)
      raise err
    end
  end

  #
  # :call-seq:
  #   ostruct[name]  -> object
  #
  # Returns the value of an attribute.
  #
  #   require "ostruct"
  #   person = OpenStruct.new("name" => "John Smith", "age" => 70)
  #   person[:age]   # => 70, same as person.age
  #
  def [](name)
    @table[name.to_sym]
  end

  #
  # :call-seq:
  #   ostruct[name] = obj  -> obj
  #
  # 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
  #
  def []=(name, value)
    modifiable?[new_ostruct_member!(name)] = value
  end

  #
  # :call-seq:
  #   ostruct.dig(name, ...)  -> object
  #
  # Extracts the nested value specified by the sequence of +name+
  # objects by calling +dig+ at each step, returning +nil+ if any
  # intermediate step is +nil+.
  #
  #   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
  #
  #   data = OpenStruct.new(:array => [1, [2, 3]])
  #
  #   data.dig(:array, 1, 0)   # => 2
  #   data.dig(:array, 0, 0)   # TypeError: Integer does not have #dig method
  #
  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

  #
  # 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>
  #
  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

  InspectKey = :__inspect_key__ # :nodoc:

  #
  # Returns a string containing a detailed summary of the keys and values.
  #
  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
  alias :to_s :inspect

  attr_reader :table # :nodoc:
  protected :table
  alias table! table

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

  # Computes a hash code for this OpenStruct.
  # Two OpenStruct objects with the same content will have the same hash code
  # (and will compare using #eql?).
  #
  # See also Object#hash.
  def hash
    @table.hash
  end
end