Module

alias_attribute(new_name, old_name)

Allows you to make aliases for attributes, which includes getter, setter, and query methods.

Example:

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"

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/aliasing.rb, line 63
def alias_attribute(new_name, old_name)
  module_eval       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, __FILE__, __LINE__ + 1
end

alias_method_chain(target, feature)

Encapsulates the common pattern of:

alias_method :foo_without_feature, :foo
alias_method :foo, :foo_with_feature

With this, you simply do:

alias_method_chain :foo, :feature

And both aliases are set up for you.

Query and bang methods (foo?, foo!) keep the same punctuation:

alias_method_chain :foo?, :feature

is equivalent to

alias_method :foo_without_feature?, :foo?
alias_method :foo?, :foo_with_feature?

so you can safely chain foo, foo?, and foo! with the same feature.

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/aliasing.rb, line 23
def alias_method_chain(target, feature)
  # Strip out punctuation on predicates or bang methods since
  # e.g. target?_without_feature is not a valid method name.
  aliased_target, punctuation = target.to_s.sub(/([?!=])$/, ''), $1
  yield(aliased_target, punctuation) if block_given?

  with_method, without_method = "#{aliased_target}_with_#{feature}#{punctuation}", "#{aliased_target}_without_#{feature}#{punctuation}"

  alias_method without_method, target
  alias_method target, with_method

  case
    when public_method_defined?(without_method)
      public target
    when protected_method_defined?(without_method)
      protected target
    when private_method_defined?(without_method)
      private target
  end
end

anonymous?()

A module may or may not have a name.

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

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

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 = m          # => m gets a name here as a side-effect
m.name         # => "M"

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/anonymous.rb, line 19
def anonymous?
  # Uses blank? because the name of an anonymous class is an empty
  # string in 1.8, and nil in 1.9.
  name.blank?
end

attr_accessor_with_default(sym, default = Proc.new)

Declare an attribute accessor with an initial default return value.

To give attribute :age the initial value 25:

class Person
  attr_accessor_with_default :age, 25
end

person = Person.new
person.age # => 25

person.age = 26
person.age # => 26

To give attribute :element_name a dynamic default value, evaluated in scope of self:

attr_accessor_with_default(:element_name) { name.underscore }

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attr_accessor_with_default.rb, line 21
def attr_accessor_with_default(sym, default = Proc.new)
  ActiveSupport::Deprecation.warn "attr_accessor_with_default is deprecated. Use Ruby instead!"
  define_method(sym, block_given? ? default : Proc.new { default })
  module_eval(      def #{sym}=(value)                          # def age=(value)        class << self; attr_accessor :#{sym} end  #   class << self; attr_accessor :age end        @#{sym} = value                           #   @age = value      end                                         # end, __FILE__, __LINE__ + 1)
end

attr_internal(*attrs)

attr_internal_accessor(*attrs)

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

This method is also aliased as attr_internal

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 14
def attr_internal_accessor(*attrs)
  attr_internal_reader(*attrs)
  attr_internal_writer(*attrs)
end

attr_internal_reader(*attrs)

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

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 3
def attr_internal_reader(*attrs)
  attrs.each {|attr_name| attr_internal_define(attr_name, :reader)}
end

attr_internal_writer(*attrs)

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

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attr_internal.rb, line 8
def attr_internal_writer(*attrs)
  attrs.each {|attr_name| attr_internal_define(attr_name, :writer)}
end

delegate(*methods)

Provides a delegate class method to easily expose contained objects’ methods as your own. Pass one or more methods (specified as symbols or strings) and the name of the target object via the :to option (also a symbol or string). At least one method and the :to option are required.

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

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"

If the delegate object is nil an exception is raised, and that happens no matter whether nil responds to the delegated method. You can get a nil instead with the :allow_nil option.

class Foo
  attr_accessor :bar
  def initialize(bar = nil)
    @bar = bar
  end
  delegate :zoo, :to => :bar
end

Foo.new.zoo   # raises NoMethodError exception (you called nil.zoo)

class Foo
  attr_accessor :bar
  def initialize(bar = nil)
    @bar = bar
  end
  delegate :zoo, :to => :bar, :allow_nil => true
end

Foo.new.zoo   # returns nil

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/delegation.rb, line 106
def delegate(*methods)
  options = methods.pop
  unless options.is_a?(Hash) && to = options[:to]
    raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, :to => :greeter)."
  end

  if options[:prefix] == true && options[:to].to_s =~ /^[^a-z_]/
    raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
  end

  prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_" || ''

  file, line = caller.first.split(':', 2)
  line = line.to_i

  methods.each do |method|
    on_nil =
      if options[:allow_nil]
        'return'
      else
        %(raise "#{self}##{prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")
      end

    module_eval(        def #{prefix}#{method}(*args, &block)               # def customer_name(*args, &block)          #{to}.__send__(#{method.inspect}, *args, &block)  #   client.__send__(:name, *args, &block)        rescue NoMethodError                                # rescue NoMethodError          if #{to}.nil?                                     #   if client.nil?            #{on_nil}                                       #     return # depends on :allow_nil          else                                              #   else            raise                                           #     raise          end                                               #   end        end                                                 # end, file, line - 1)
  end
end

deprecate(*method_names)

Declare that a method has been deprecated.

deprecate :foo
deprecate :bar => 'message'
deprecate :foo, :bar, :baz => 'warning!', :qux => 'gone!'

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/deprecation.rb, line 6
def deprecate(*method_names)
  ActiveSupport::Deprecation.deprecate_methods(self, *method_names)
end

duplicable?()

Modules are not duplicable:

m = Module.new # => #<Module:0x10328b6e0>
m.dup          # => #<Module:0x10328b6e0>

Note dup returned the same module object.

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/object/duplicable.rb, line 103
def duplicable?
  false
end

instance_method_names(*args)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/method_names.rb, line 3
def instance_method_names(*args)
  instance_methods(*args).map(&:to_s)
end

local_constant_names()

Returns the names of the constants defined locally rather than the constants themselves. See local_constants.

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 85
def local_constant_names
  local_constants.map { |c| c.to_s }
end

local_constants()

Returns the constants that have been defined locally by this object and not in an ancestor. This method is exact if running under Ruby 1.9. In previous versions it may miss some constants if their definition in some ancestor is identical to their definition in the receiver.

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 65
def local_constants
  inherited = {}

  ancestors.each do |anc|
    next if anc == self
    anc.constants.each { |const| inherited[const] = anc.const_get(const) }
  end

  constants.select do |const|
    !inherited.key?(const) || inherited[const].object_id != const_get(const).object_id
  end
end

mattr_accessor(*syms)

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

module AppConfiguration
  mattr_accessor :google_api_key
  self.google_api_key = "123456789"

  mattr_accessor :paypal_url
  self.paypal_url = "www.sandbox.paypal.com"
end

AppConfiguration.google_api_key = "overriding the api key!"

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 56
def mattr_accessor(*syms)
  mattr_reader(*syms)
  mattr_writer(*syms)
end

mattr_reader(*syms)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 4
def mattr_reader(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval(        @@#{sym} = nil unless defined? @@#{sym}        def self.#{sym}          @@#{sym}        end, __FILE__, __LINE__ + 1)

    unless options[:instance_reader] == false
      class_eval(          def #{sym}            @@#{sym}          end, __FILE__, __LINE__ + 1)
    end
  end
end

mattr_writer(*syms)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 25
def mattr_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    class_eval(        def self.#{sym}=(obj)          @@#{sym} = obj        end, __FILE__, __LINE__ + 1)

    unless options[:instance_writer] == false
      class_eval(          def #{sym}=(obj)            @@#{sym} = obj          end, __FILE__, __LINE__ + 1)
    end
  end
end

method_names(*args)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/method_names.rb, line 7
def method_names(*args)
  methods(*args).map(&:to_s)
end

parent()

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

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

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

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

M.parent          # => Object
Module.new.parent # => Object

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 30
def parent
  parent_name ? ActiveSupport::Inflector.constantize(parent_name) : Object
end

parent_name()

Returns the name of the module containing this one.

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

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 7
def parent_name
  unless defined? @parent_name
    @parent_name = name =~ /::[^:]+\Z/ ? $`.freeze : nil
  end
  @parent_name
end

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.parents    # => [Object]
M::N.parents # => [M, Object]
X.parents    # => [M, Object]

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/introspection.rb, line 47
def parents
  parents = []
  if parent_name
    parts = 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)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/remove_method.rb, line 12
def redefine_method(method, &block)
  remove_possible_method(method)
  define_method(method, &block)
end

remove_possible_method(method)

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/remove_method.rb, line 2
def remove_possible_method(method)
  if method_defined?(method) || private_method_defined?(method)
    remove_method(method)
  end
rescue NameError
  # If the requested method is defined on a superclass or included module,
  # method_defined? returns true but remove_method throws a NameError.
  # Ignore this.
end

synchronize(*methods)

Synchronize access around a method, delegating synchronization to a particular mutex. A mutex (either a Mutex, or any object that responds to synchronize and yields to a block) must be provided as a final :with option. The :with option should be a symbol or string, and can represent a method, constant, or instance or class variable. Example:

class SharedCache
  @@lock = Mutex.new
  def expire
    ...
  end
  synchronize :expire, :with => :@@lock
end

Source: show | on GitHub

# File activesupport/lib/active_support/core_ext/module/synchronization.rb, line 19
def synchronize(*methods)
  options = methods.extract_options!
  unless options.is_a?(Hash) && with = options[:with]
    raise ArgumentError, "Synchronization needs a mutex. Supply an options hash with a :with key as the last argument (e.g. synchronize :hello, :with => :@mutex)."
  end

  methods.each do |method|
    aliased_method, punctuation = method.to_s.sub(/([?!=])$/, ''), $1

    if method_defined?("#{aliased_method}_without_synchronization#{punctuation}")
      raise ArgumentError, "#{method} is already synchronized. Double synchronization is not currently supported."
    end

    module_eval(        def #{aliased_method}_with_synchronization#{punctuation}(*args, &block)     # def expire_with_synchronization(*args, &block)          #{with}.synchronize do                                                    #   @@lock.synchronize do            #{aliased_method}_without_synchronization#{punctuation}(*args, &block)  #     expire_without_synchronization(*args, &block)          end                                                                       #   end        end                                                                         # end, __FILE__, __LINE__ + 1)

    alias_method_chain method, :synchronization
  end
end

Class Module < Object