Class: Module

Inherits:
Object show all
Includes:
Concerning
Defined in:
lib/active_support/core_ext/module/attribute_accessors.rb,
lib/active_support/core_ext/object/json.rb,
lib/active_support/core_ext/module/aliasing.rb,
lib/active_support/core_ext/object/deep_dup.rb,
lib/active_support/core_ext/module/anonymous.rb,
lib/active_support/core_ext/module/concerning.rb,
lib/active_support/core_ext/module/delegation.rb,
lib/active_support/core_ext/module/deprecation.rb,
lib/active_support/core_ext/module/attr_internal.rb,
lib/active_support/core_ext/module/introspection.rb,
lib/active_support/core_ext/module/remove_method.rb,
lib/active_support/core_ext/module/redefine_method.rb,
lib/active_support/core_ext/module/attribute_accessors_per_thread.rb

Overview

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.

Defined Under Namespace

Modules: Concerning

Constant Summary collapse

DelegationError =

:nodoc:

ActiveSupport::DelegationError

Class Attribute Summary collapse

Instance Method Summary collapse

Methods included from Concerning

#concern, #concerning

Class Attribute Details

.attr_internal_naming_format ⇒ Object

Returns the value of attribute attr_internal_naming_format.



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# File 'lib/active_support/core_ext/module/attr_internal.rb', line 23

def attr_internal_naming_format
  @attr_internal_naming_format
end

Instance Method Details

#alias_attribute(new_name, old_name) ⇒ Object

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"



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# File '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

#anonymous? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/active_support/core_ext/module/anonymous.rb', line 27

def anonymous?
  name.nil?
end

#as_json(options = nil) ⇒ Object

:nodoc:



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# File 'lib/active_support/core_ext/object/json.rb', line 53

def as_json(options = nil) # :nodoc:
  name
end

#attr_internal_accessor(*attrs) ⇒ Object Also known as: attr_internal

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



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# File '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

#attr_internal_reader(*attrs) ⇒ Object

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



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# File '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

#attr_internal_writer(*attrs) ⇒ Object

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



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# File '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

#deep_dup ⇒ Object

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



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# File 'lib/active_support/core_ext/object/deep_dup.rb', line 64

def deep_dup
  if name.nil?
    super
  else
    self
  end
end

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

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 ActiveSupport::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 ActiveSupport::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
# => ActiveSupport::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.



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# File 'lib/active_support/core_ext/module/delegation.rb', line 160

def delegate(*methods, to: nil, prefix: nil, allow_nil: nil, private: nil)
  ::ActiveSupport::Delegation.generate(
    self,
    methods,
    location: caller_locations(1, 1).first,
    to: to,
    prefix: prefix,
    allow_nil: allow_nil,
    private: private,
  )
end

#delegate_missing_to(target, allow_nil: nil) ⇒ Object

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 ActiveSupport::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.



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# File 'lib/active_support/core_ext/module/delegation.rb', line 218

def delegate_missing_to(target, allow_nil: nil)
  ::ActiveSupport::Delegation.generate_method_missing(
    self,
    target,
    allow_nil: allow_nil,
  )
end

#deprecate(*method_names, deprecator:, **options) ⇒ Object

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



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# File 'lib/active_support/core_ext/module/deprecation.rb', line 17

def deprecate(*method_names, deprecator:, **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)
  end
end

#mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk) ⇒ Object Also known as: cattr_accessor

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]



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# File '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

#mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil) ⇒ Object Also known as: cattr_reader

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]

Raises:

  • (TypeError) 


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# File '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

#mattr_writer(*syms, instance_writer: true, instance_accessor: true, default: nil, location: nil) ⇒ Object Also known as: cattr_writer

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]

Raises:

  • (TypeError) 


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# File '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

#method_visibility(method) ⇒ Object

:nodoc:



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# File 'lib/active_support/core_ext/module/redefine_method.rb', line 30

def method_visibility(method) # :nodoc:
  case
  when private_method_defined?(method)
    :private
  when protected_method_defined?(method)
    :protected
  else
    :public
  end
end

#module_parent ⇒ Object

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



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# File 'lib/active_support/core_ext/module/introspection.rb', line 34

def module_parent
  module_parent_name ? ActiveSupport::Inflector.constantize(module_parent_name) : Object
end

#module_parent_name ⇒ Object

Returns the name of the module containing this one.

M::N.module_parent_name # => "M"



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# File '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

#module_parents ⇒ Object

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]



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# File '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

#redefine_method(method, &block) ⇒ Object

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



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# File '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

#redefine_singleton_method(method, &block) ⇒ Object

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



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# File 'lib/active_support/core_ext/module/redefine_method.rb', line 26

def redefine_singleton_method(method, &block)
  singleton_class.redefine_method(method, &block)
end

#remove_possible_method(method) ⇒ Object

Removes the named method, if it exists.



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# File '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

#remove_possible_singleton_method(method) ⇒ Object

Removes the named singleton method, if it exists.



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# File 'lib/active_support/core_ext/module/remove_method.rb', line 14

def remove_possible_singleton_method(method)
  singleton_class.remove_possible_method(method)
end

#silence_redefinition_of_method(method) ⇒ Object

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



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# File '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

#thread_mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil) ⇒ Object Also known as: thread_cattr_accessor

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.



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# File '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

#thread_mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil) ⇒ Object Also known as: thread_cattr_reader

Defines a per-thread class attribute and creates class and instance reader methods. The underlying per-thread class variable is set to nil, if it is not previously defined.

module Current
  thread_mattr_reader :user
end

Current.user = "DHH"
Current.user # => "DHH"
Thread.new { Current.user }.value # => nil

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

module Foo
  thread_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.

class Current
  thread_mattr_reader :user, instance_reader: false
end

Current.new.user # => NoMethodError



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# File 'lib/active_support/core_ext/module/attribute_accessors_per_thread.rb', line 41

def thread_mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil) # :nodoc:
  syms.each do |sym|
    raise NameError.new("invalid attribute name: #{sym}") unless /^[_A-Za-z]\w*$/.match?(sym)

    # The following generated method concatenates `object_id` because we want
    # subclasses to maintain independent values.
    if default.nil?
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def self.#{sym}
          @__thread_mattr_#{sym} ||= "attr_#{sym}_\#{object_id}"
          ::ActiveSupport::IsolatedExecutionState[@__thread_mattr_#{sym}]
        end
      EOS
    else
      default = default.dup.freeze unless default.frozen?
      singleton_class.define_method("#{sym}_default_value") { default }

      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def self.#{sym}
          @__thread_mattr_#{sym} ||= "attr_#{sym}_\#{object_id}"
          value = ::ActiveSupport::IsolatedExecutionState[@__thread_mattr_#{sym}]

          if value.nil? && !::ActiveSupport::IsolatedExecutionState.key?(@__thread_mattr_#{sym})
            ::ActiveSupport::IsolatedExecutionState[@__thread_mattr_#{sym}] = #{sym}_default_value
          else
            value
          end
        end
      EOS
    end

    if instance_reader && instance_accessor
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}
          self.class.#{sym}
        end
      EOS
    end
  end
end

#thread_mattr_writer(*syms, instance_writer: true, instance_accessor: true) ⇒ Object Also known as: thread_cattr_writer

Defines a per-thread class attribute and creates a class and instance writer methods to allow assignment to the attribute.

module Current
  thread_mattr_writer :user
end

Current.user = "DHH"
Thread.current[:attr_Current_user] # => "DHH"

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

class Current
  thread_mattr_writer :user, instance_writer: false
end

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



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# File 'lib/active_support/core_ext/module/attribute_accessors_per_thread.rb', line 101

def thread_mattr_writer(*syms, instance_writer: true, instance_accessor: true) # :nodoc:
  syms.each do |sym|
    raise NameError.new("invalid attribute name: #{sym}") unless /^[_A-Za-z]\w*$/.match?(sym)

    # The following generated method concatenates `object_id` because we want
    # subclasses to maintain independent values.
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def self.#{sym}=(obj)
        @__thread_mattr_#{sym} ||= "attr_#{sym}_\#{object_id}"
        ::ActiveSupport::IsolatedExecutionState[@__thread_mattr_#{sym}] = obj
      end
    EOS

    if instance_writer && instance_accessor
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}=(obj)
          self.class.#{sym} = obj
        end
      EOS
    end
  end
end