Attribute Accessors

Extends the module object with class/module and instance accessors for class/module attributes, just like the native attr* accessors for instance attributes.

Attribute Accessors per Thread

Extends the module object with class/module and instance accessors for class/module attributes, just like the native attr* accessors for instance attributes, but does so on a per-thread basis.

So the values are scoped within the Thread.current space under the class name of the module.

Note that it can also be scoped per-fiber if Rails.application.config.active_support.isolation_level is set to :fiber.

Namespace

Module

Class

Methods

Included Modules

Constants

DELEGATION_RESERVED_KEYWORDS = %w(_ arg args block)
DELEGATION_RESERVED_METHOD_NAMES = Set.new( RUBY_RESERVED_KEYWORDS + DELEGATION_RESERVED_KEYWORDS ).freeze
RUBY_RESERVED_KEYWORDS = %w(__ENCODING__ __LINE__ __FILE__ alias and BEGIN begin break case class def defined? do else elsif END end ensure false for if in module next nil not or redo rescue retry return self super then true undef unless until when while yield)

Attributes

[RW] attr_internal_naming_format

Instance Public methods

alias_attribute(new_name, old_name)

Allows you to make aliases for attributes, which includes getter, setter, and a predicate.

class Content < ActiveRecord::Base
  # has a title attribute
end

class Email < Content
  alias_attribute :subject, :title
end

e = Email.find(1)
e.title    # => "Superstars"
e.subject  # => "Superstars"
e.subject? # => true
e.subject = "Megastars"
e.title    # => "Megastars"
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/aliasing.rb, line 21
  def alias_attribute(new_name, old_name)
    # The following reader methods use an explicit `self` receiver in order to
    # support aliases that start with an uppercase letter. Otherwise, they would
    # be resolved as constants instead.
    module_eval <<-STR, __FILE__, __LINE__ + 1
      def #{new_name}; self.#{old_name}; end          # def subject; self.title; end
      def #{new_name}?; self.#{old_name}?; end        # def subject?; self.title?; end
      def #{new_name}=(v); self.#{old_name} = v; end  # def subject=(v); self.title = v; end
    STR
  end
πŸ”Ž See on GitHub

anonymous?()

A module may or may not have a name.

module M; end
M.name # => "M"

m = Module.new
m.name # => nil

anonymous? method returns true if module does not have a name, false otherwise:

Module.new.anonymous? # => true

module M; end
M.anonymous?          # => false

A module gets a name when it is first assigned to a constant. Either via the module or class keyword or by an explicit assignment:

m = Module.new # creates an anonymous module
m.anonymous?   # => true
M = m          # m gets a name here as a side-effect
m.name         # => "M"
m.anonymous?   # => false
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/anonymous.rb, line 27
  def anonymous?
    name.nil?
  end
πŸ”Ž See on GitHub

attr_internal(*attrs)

attr_internal_accessor(*attrs)

Declares an attribute reader and writer backed by an internally-named instance variable.

Also aliased as: attr_internal
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 16
  def attr_internal_accessor(*attrs)
    attr_internal_reader(*attrs)
    attr_internal_writer(*attrs)
  end
πŸ”Ž See on GitHub

attr_internal_reader(*attrs)

Declares an attribute reader backed by an internally-named instance variable.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 5
  def attr_internal_reader(*attrs)
    attrs.each { |attr_name| attr_internal_define(attr_name, :reader) }
  end
πŸ”Ž See on GitHub

attr_internal_writer(*attrs)

Declares an attribute writer backed by an internally-named instance variable.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 10
  def attr_internal_writer(*attrs)
    attrs.each { |attr_name| attr_internal_define(attr_name, :writer) }
  end
πŸ”Ž See on GitHub

cattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)

Alias for: mattr_accessor

cattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil)

Alias for: mattr_reader

cattr_writer(*syms, instance_writer: true, instance_accessor: true, default: nil, location: nil)

Alias for: mattr_writer

deep_dup()

Returns a copy of module or class if it’s anonymous. If it’s named, returns self.

Object.deep_dup == Object # => true
klass = Class.new
klass.deep_dup == klass # => false
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/object/deep_dup.rb, line 64
  def deep_dup
    if name.nil?
      super
    else
      self
    end
  end
πŸ”Ž See on GitHub

delegate(*methods, to: nil, prefix: nil, allow_nil: nil, private: nil)

Provides a delegate class method to easily expose contained objects’ public methods as your own.

Options

  • :to - Specifies the target object name as a symbol or string

  • :prefix - Prefixes the new method with the target name or a custom prefix

  • :allow_nil - If set to true, prevents a Module::DelegationError from being raised

  • :private - If set to true, changes method visibility to private

The macro receives one or more method names (specified as symbols or strings) and the name of the target object via the :to option (also a symbol or string).

Delegation is particularly useful with Active Record associations:

class Greeter < ActiveRecord::Base
  def hello
    'hello'
  end

  def goodbye
    'goodbye'
  end
end

class Foo < ActiveRecord::Base
  belongs_to :greeter
  delegate :hello, to: :greeter
end

Foo.new.hello   # => "hello"
Foo.new.goodbye # => NoMethodError: undefined method `goodbye' for #<Foo:0x1af30c>

Multiple delegates to the same target are allowed:

class Foo < ActiveRecord::Base
  belongs_to :greeter
  delegate :hello, :goodbye, to: :greeter
end

Foo.new.goodbye # => "goodbye"

Methods can be delegated to instance variables, class variables, or constants by providing them as a symbols:

class Foo
  CONSTANT_ARRAY = [0,1,2,3]
  @@class_array  = [4,5,6,7]

  def initialize
    @instance_array = [8,9,10,11]
  end
  delegate :sum, to: :CONSTANT_ARRAY
  delegate :min, to: :@@class_array
  delegate :max, to: :@instance_array
end

Foo.new.sum # => 6
Foo.new.min # => 4
Foo.new.max # => 11

It’s also possible to delegate a method to the class by using :class:

class Foo
  def self.hello
    "world"
  end

  delegate :hello, to: :class
end

Foo.new.hello # => "world"

Delegates can optionally be prefixed using the :prefix option. If the value is true, the delegate methods are prefixed with the name of the object being delegated to.

Person = Struct.new(:name, :address)

class Invoice < Struct.new(:client)
  delegate :name, :address, to: :client, prefix: true
end

john_doe = Person.new('John Doe', 'Vimmersvej 13')
invoice = Invoice.new(john_doe)
invoice.client_name    # => "John Doe"
invoice.client_address # => "Vimmersvej 13"

It is also possible to supply a custom prefix.

class Invoice < Struct.new(:client)
  delegate :name, :address, to: :client, prefix: :customer
end

invoice = Invoice.new(john_doe)
invoice.customer_name    # => 'John Doe'
invoice.customer_address # => 'Vimmersvej 13'

The delegated methods are public by default. Pass private: true to change that.

class User < ActiveRecord::Base
  has_one :profile
  delegate :first_name, to: :profile
  delegate :date_of_birth, to: :profile, private: true

  def age
    Date.today.year - date_of_birth.year
  end
end

User.new.first_name # => "Tomas"
User.new.date_of_birth # => NoMethodError: private method `date_of_birth' called for #<User:0x00000008221340>
User.new.age # => 2

If the target is nil and does not respond to the delegated method a Module::DelegationError is raised. If you wish to instead return nil, use the :allow_nil option.

class User < ActiveRecord::Base
  has_one :profile
  delegate :age, to: :profile
end

User.new.age
# => Module::DelegationError: User#age delegated to profile.age, but profile is nil

But if not having a profile yet is fine and should not be an error condition:

class User < ActiveRecord::Base
  has_one :profile
  delegate :age, to: :profile, allow_nil: true
end

User.new.age # nil

Note that if the target is not nil then the call is attempted regardless of the :allow_nil option, and thus an exception is still raised if said object does not respond to the method:

class Foo
  def initialize(bar)
    @bar = bar
  end

  delegate :name, to: :@bar, allow_nil: true
end

Foo.new("Bar").name # raises NoMethodError: undefined method `name'

The target method must be public, otherwise it will raise NoMethodError.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/delegation.rb, line 171
  def delegate(*methods, to: nil, prefix: nil, allow_nil: nil, private: nil)
    unless to
      raise ArgumentError, "Delegation needs a target. Supply a keyword argument 'to' (e.g. delegate :hello, to: :greeter)."
    end

    if prefix == true && /^[^a-z_]/.match?(to)
      raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
    end

    method_prefix = \
      if prefix
        "#{prefix == true ? to : prefix}_"
      else
        ""
      end

    location = caller_locations(1, 1).first
    file, line = location.path, location.lineno

    receiver = to.to_s
    receiver = "self.#{receiver}" if DELEGATION_RESERVED_METHOD_NAMES.include?(receiver)

    method_def = []
    method_names = []

    method_def << "self.private" if private

    methods.each do |method|
      method_name = prefix ? "#{method_prefix}#{method}" : method
      method_names << method_name.to_sym

      # Attribute writer methods only accept one argument. Makes sure []=
      # methods still accept two arguments.
      definition = \
        if /[^\]]=\z/.match?(method)
          "arg"
        else
          method_object =
            begin
              if to.is_a?(Module)
                to.method(method)
              elsif receiver == "self.class"
                method(method)
              end
            rescue NameError
              # Do nothing. Fall back to `"..."`
            end

          if method_object
            parameters = method_object.parameters

            if (parameters.map(&:first) & [:opt, :rest, :keyreq, :key, :keyrest]).any?
              "..."
            else
              defn = parameters.filter_map { |type, arg| arg if type == :req }
              defn << "&block"
              defn.join(", ")
            end
          else
            "..."
          end
        end

      # The following generated method calls the target exactly once, storing
      # the returned value in a dummy variable.
      #
      # Reason is twofold: On one hand doing less calls is in general better.
      # On the other hand it could be that the target has side-effects,
      # whereas conceptually, from the user point of view, the delegator should
      # be doing one call.
      if allow_nil
        method = method.to_s

        method_def <<
          "def #{method_name}(#{definition})" <<
          "  _ = #{receiver}" <<
          "  if !_.nil? || nil.respond_to?(:#{method})" <<
          "    _.#{method}(#{definition})" <<
          "  end" <<
          "end"
      else
        method = method.to_s
        method_name = method_name.to_s

        method_def <<
          "def #{method_name}(#{definition})" <<
          "  _ = #{receiver}" <<
          "  _.#{method}(#{definition})" <<
          "rescue NoMethodError => e" <<
          "  if _.nil? && e.name == :#{method}" <<
          %(   raise DelegationError, "#{self}##{method_name} delegated to #{receiver}.#{method}, but #{receiver} is nil: \#{self.inspect}") <<
          "  else" <<
          "    raise" <<
          "  end" <<
          "end"
      end
    end
    module_eval(method_def.join(";"), file, line)
    method_names
  end
πŸ”Ž See on GitHub

delegate_missing_to(target, allow_nil: nil)

When building decorators, a common pattern may emerge:

class Partition
  def initialize(event)
    @event = event
  end

  def person
    detail.person || creator
  end

  private
    def respond_to_missing?(name, include_private = false)
      @event.respond_to?(name, include_private)
    end

    def method_missing(method, *args, &block)
      @event.send(method, *args, &block)
    end
end

With Module#delegate_missing_to, the above is condensed to:

class Partition
  delegate_missing_to :@event

  def initialize(event)
    @event = event
  end

  def person
    detail.person || creator
  end
end

The target can be anything callable within the object, e.g. instance variables, methods, constants, etc.

The delegated method must be public on the target, otherwise it will raise DelegationError. If you wish to instead return nil, use the :allow_nil option.

The marshal_dump and _dump methods are exempt from delegation due to possible interference when calling Marshal.dump(object), should the delegation target method of object add or remove instance variables.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/delegation.rb, line 318
  def delegate_missing_to(target, allow_nil: nil)
    target = target.to_s
    target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target)

    module_eval <<-RUBY, __FILE__, __LINE__ + 1
      def respond_to_missing?(name, include_private = false)
        # It may look like an oversight, but we deliberately do not pass
        # +include_private+, because they do not get delegated.

        return false if name == :marshal_dump || name == :_dump
        #{target}.respond_to?(name) || super
      end

      def method_missing(method, *args, &block)
        if #{target}.respond_to?(method)
          #{target}.public_send(method, *args, &block)
        else
          begin
            super
          rescue NoMethodError
            if #{target}.nil?
              if #{allow_nil == true}
                nil
              else
                raise DelegationError, "\#{method} delegated to #{target}, but #{target} is nil"
              end
            else
              raise
            end
          end
        end
      end
      ruby2_keywords(:method_missing)
    RUBY
  end
πŸ”Ž See on GitHub

deprecate(*method_names, deprecator: nil, **options)

deprecate :foo, deprecator: MyLib.deprecator
deprecate :foo, bar: "warning!", deprecator: MyLib.deprecator

A deprecator is typically an instance of ActiveSupport::Deprecation, but you can also pass any object that responds to deprecation_warning(deprecated_method_name, message, caller_backtrace) where you can implement your custom warning behavior.

class MyLib::Deprecator
  def deprecation_warning(deprecated_method_name, message, caller_backtrace = nil)
    message = "#{deprecated_method_name} is deprecated and will be removed from MyLibrary | #{message}"
    Kernel.warn message
  end
end
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/deprecation.rb, line 17
  def deprecate(*method_names, deprecator: nil, **options)
    if deprecator.is_a?(ActiveSupport::Deprecation)
      deprecator.deprecate_methods(self, *method_names, **options)
    elsif deprecator
      # we just need any instance to call deprecate_methods, but the deprecation will be emitted by deprecator
      ActiveSupport.deprecator.deprecate_methods(self, *method_names, **options, deprecator: deprecator)
    else
      ActiveSupport.deprecator.warn("Module.deprecate without a deprecator is deprecated")
      ActiveSupport::Deprecation._instance.deprecate_methods(self, *method_names, **options)
    end
  end
πŸ”Ž See on GitHub

mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)

Defines both class and instance accessors for class attributes. All class and instance methods created will be public, even if this method is called with a private or protected access modifier.

module HairColors
  mattr_accessor :hair_colors
end

class Person
  include HairColors
end

HairColors.hair_colors = [:brown, :black, :blonde, :red]
HairColors.hair_colors # => [:brown, :black, :blonde, :red]
Person.new.hair_colors # => [:brown, :black, :blonde, :red]

If a subclass changes the value then that would also change the value for parent class. Similarly if parent class changes the value then that would change the value of subclasses too.

class Citizen < Person
end

Citizen.new.hair_colors << :blue
Person.new.hair_colors # => [:brown, :black, :blonde, :red, :blue]

To omit the instance writer method, pass instance_writer: false. To omit the instance reader method, pass instance_reader: false.

module HairColors
  mattr_accessor :hair_colors, instance_writer: false, instance_reader: false
end

class Person
  include HairColors
end

Person.new.hair_colors = [:brown]  # => NoMethodError
Person.new.hair_colors             # => NoMethodError

Or pass instance_accessor: false, to omit both instance methods.

module HairColors
  mattr_accessor :hair_colors, instance_accessor: false
end

class Person
  include HairColors
end

Person.new.hair_colors = [:brown]  # => NoMethodError
Person.new.hair_colors             # => NoMethodError

You can set a default value for the attribute.

module HairColors
  mattr_accessor :hair_colors, default: [:brown, :black, :blonde, :red]
  mattr_accessor(:hair_styles) { [:long, :short] }
end

class Person
  include HairColors
end

Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]
Person.class_variable_get("@@hair_styles") # => [:long, :short]
Also aliased as: cattr_accessor
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 208
  def mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)
    location = caller_locations(1, 1).first
    mattr_reader(*syms, instance_reader: instance_reader, instance_accessor: instance_accessor, default: default, location: location, &blk)
    mattr_writer(*syms, instance_writer: instance_writer, instance_accessor: instance_accessor, default: default, location: location)
  end
πŸ”Ž See on GitHub

mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil)

Defines a class attribute and creates a class and instance reader methods. The underlying class variable is set to nil, if it is not previously defined. All class and instance methods created will be public, even if this method is called with a private or protected access modifier.

module HairColors
  mattr_reader :hair_colors
end

HairColors.hair_colors # => nil
HairColors.class_variable_set("@@hair_colors", [:brown, :black])
HairColors.hair_colors # => [:brown, :black]

The attribute name must be a valid method name in Ruby.

module Foo
  mattr_reader :"1_Badname"
end
# => NameError: invalid attribute name: 1_Badname

To omit the instance reader method, pass instance_reader: false or instance_accessor: false.

module HairColors
  mattr_reader :hair_colors, instance_reader: false
end

class Person
  include HairColors
end

Person.new.hair_colors # => NoMethodError

You can set a default value for the attribute.

module HairColors
  mattr_reader :hair_colors, default: [:brown, :black, :blonde, :red]
  mattr_reader(:hair_styles) { [:long, :short] }
end

class Person
  include HairColors
end

Person.new.hair_colors # => [:brown, :black, :blonde, :red]
Person.new.hair_styles # => [:long, :short]
Also aliased as: cattr_reader
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 55
  def mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil)
    raise TypeError, "module attributes should be defined directly on class, not singleton" if singleton_class?
    location ||= caller_locations(1, 1).first

    definition = []
    syms.each do |sym|
      raise NameError.new("invalid attribute name: #{sym}") unless /\A[_A-Za-z]\w*\z/.match?(sym)

      definition << "def self.#{sym}; @@#{sym}; end"

      if instance_reader && instance_accessor
        definition << "def #{sym}; @@#{sym}; end"
      end

      sym_default_value = (block_given? && default.nil?) ? yield : default
      class_variable_set("@@#{sym}", sym_default_value) unless sym_default_value.nil? && class_variable_defined?("@@#{sym}")
    end

    module_eval(definition.join(";"), location.path, location.lineno)
  end
πŸ”Ž See on GitHub

mattr_writer(*syms, instance_writer: true, instance_accessor: true, default: nil, location: nil)

Defines a class attribute and creates a class and instance writer methods to allow assignment to the attribute. All class and instance methods created will be public, even if this method is called with a private or protected access modifier.

module HairColors
  mattr_writer :hair_colors
end

class Person
  include HairColors
end

HairColors.hair_colors = [:brown, :black]
Person.class_variable_get("@@hair_colors") # => [:brown, :black]
Person.new.hair_colors = [:blonde, :red]
HairColors.class_variable_get("@@hair_colors") # => [:blonde, :red]

To omit the instance writer method, pass instance_writer: false or instance_accessor: false.

module HairColors
  mattr_writer :hair_colors, instance_writer: false
end

class Person
  include HairColors
end

Person.new.hair_colors = [:blonde, :red] # => NoMethodError

You can set a default value for the attribute.

module HairColors
  mattr_writer :hair_colors, default: [:brown, :black, :blonde, :red]
  mattr_writer(:hair_styles) { [:long, :short] }
end

class Person
  include HairColors
end

Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]
Person.class_variable_get("@@hair_styles") # => [:long, :short]
Also aliased as: cattr_writer
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 121
  def mattr_writer(*syms, instance_writer: true, instance_accessor: true, default: nil, location: nil)
    raise TypeError, "module attributes should be defined directly on class, not singleton" if singleton_class?
    location ||= caller_locations(1, 1).first

    definition = []
    syms.each do |sym|
      raise NameError.new("invalid attribute name: #{sym}") unless /\A[_A-Za-z]\w*\z/.match?(sym)
      definition << "def self.#{sym}=(val); @@#{sym} = val; end"

      if instance_writer && instance_accessor
        definition << "def #{sym}=(val); @@#{sym} = val; end"
      end

      sym_default_value = (block_given? && default.nil?) ? yield : default
      class_variable_set("@@#{sym}", sym_default_value) unless sym_default_value.nil? && class_variable_defined?("@@#{sym}")
    end

    module_eval(definition.join(";"), location.path, location.lineno)
  end
πŸ”Ž See on GitHub

module_parent()

Returns the module which contains this one according to its name.

module M
  module N
  end
end
X = M::N

M::N.module_parent # => M
X.module_parent    # => M

The parent of top-level and anonymous modules is Object.

M.module_parent          # => Object
Module.new.module_parent # => Object
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 34
  def module_parent
    module_parent_name ? ActiveSupport::Inflector.constantize(module_parent_name) : Object
  end
πŸ”Ž See on GitHub

module_parent_name()

Returns the name of the module containing this one.

M::N.module_parent_name # => "M"
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 9
  def module_parent_name
    if defined?(@parent_name)
      @parent_name
    else
      parent_name = name =~ /::[^:]+\z/ ? -$` : nil
      @parent_name = parent_name unless frozen?
      parent_name
    end
  end
πŸ”Ž See on GitHub

module_parents()

Returns all the parents of this module according to its name, ordered from nested outwards. The receiver is not contained within the result.

module M
  module N
  end
end
X = M::N

M.module_parents    # => [Object]
M::N.module_parents # => [M, Object]
X.module_parents    # => [M, Object]
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 50
  def module_parents
    parents = []
    if module_parent_name
      parts = module_parent_name.split("::")
      until parts.empty?
        parents << ActiveSupport::Inflector.constantize(parts * "::")
        parts.pop
      end
    end
    parents << Object unless parents.include? Object
    parents
  end
πŸ”Ž See on GitHub

redefine_method(method, &block)

Replaces the existing method definition, if there is one, with the passed block as its body.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/redefine_method.rb, line 17
  def redefine_method(method, &block)
    visibility = method_visibility(method)
    silence_redefinition_of_method(method)
    define_method(method, &block)
    send(visibility, method)
  end
πŸ”Ž See on GitHub

redefine_singleton_method(method, &block)

Replaces the existing singleton method definition, if there is one, with the passed block as its body.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/redefine_method.rb, line 26
  def redefine_singleton_method(method, &block)
    singleton_class.redefine_method(method, &block)
  end
πŸ”Ž See on GitHub

remove_possible_method(method)

Removes the named method, if it exists.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/remove_method.rb, line 7
  def remove_possible_method(method)
    if method_defined?(method) || private_method_defined?(method)
      undef_method(method)
    end
  end
πŸ”Ž See on GitHub

remove_possible_singleton_method(method)

Removes the named singleton method, if it exists.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/remove_method.rb, line 14
  def remove_possible_singleton_method(method)
    singleton_class.remove_possible_method(method)
  end
πŸ”Ž See on GitHub

silence_redefinition_of_method(method)

Marks the named method as intended to be redefined, if it exists. Suppresses the Ruby method redefinition warning. Prefer redefine_method where possible.

πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/redefine_method.rb, line 7
  def silence_redefinition_of_method(method)
    if method_defined?(method) || private_method_defined?(method)
      # This suppresses the "method redefined" warning; the self-alias
      # looks odd, but means we don't need to generate a unique name
      alias_method method, method
    end
  end
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thread_cattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil)

thread_mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil)

Defines both class and instance accessors for class attributes.

class Account
  thread_mattr_accessor :user
end

Account.user = "DHH"
Account.user     # => "DHH"
Account.new.user # => "DHH"

Unlike mattr_accessor, values are not shared with subclasses or parent classes. If a subclass changes the value, the parent class’ value is not changed. If the parent class changes the value, the value of subclasses is not changed.

class Customer < Account
end

Account.user   # => "DHH"
Customer.user  # => nil
Customer.user  = "Rafael"
Customer.user  # => "Rafael"
Account.user   # => "DHH"

To omit the instance writer method, pass instance_writer: false. To omit the instance reader method, pass instance_reader: false.

class Current
  thread_mattr_accessor :user, instance_writer: false, instance_reader: false
end

Current.new.user = "DHH"  # => NoMethodError
Current.new.user          # => NoMethodError

Or pass instance_accessor: false, to omit both instance methods.

class Current
  thread_mattr_accessor :user, instance_accessor: false
end

Current.new.user = "DHH"  # => NoMethodError
Current.new.user          # => NoMethodError

A default value may be specified using the :default option. Because multiple threads can access the default value, non-frozen default values will be duped and frozen.

Also aliased as: thread_cattr_accessor
πŸ“ Source code
# File activesupport/lib/active_support/core_ext/module/attribute_accessors_per_thread.rb, line 170
  def thread_mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil)
    thread_mattr_reader(*syms, instance_reader: instance_reader, instance_accessor: instance_accessor, default: default)
    thread_mattr_writer(*syms, instance_writer: instance_writer, instance_accessor: instance_accessor)
  end
πŸ”Ž See on GitHub