Class: Module

Inherits:
Object show all
Defined in:
activesupport/lib/active_support/core_ext/module/qualified_const.rb,
activesupport/lib/active_support/core_ext/module/aliasing.rb,
activesupport/lib/active_support/core_ext/module/reachable.rb,
activesupport/lib/active_support/core_ext/module/anonymous.rb,
activesupport/lib/active_support/core_ext/module/delegation.rb,
activesupport/lib/active_support/core_ext/module/deprecation.rb,
activesupport/lib/active_support/core_ext/module/remove_method.rb,
activesupport/lib/active_support/core_ext/module/introspection.rb,
activesupport/lib/active_support/core_ext/module/attr_internal.rb,
activesupport/lib/active_support/core_ext/module/attribute_accessors.rb,
activesupport/lib/active_support/core_ext/module/method_transplanting.rb

Overview

Extends the API for constants to be able to deal with qualified names. Arguments are assumed to be relative to the receiver.

– Qualified names are required to be relative because we are extending existing methods that expect constant names, ie, relative paths of length 1. For example, Object.const_get('::String') raises NameError and so does qualified_const_get. ++

Defined Under Namespace

Classes: DelegationError

Class Attribute Summary collapse

Instance Method Summary collapse

Class Attribute Details

.attr_internal_naming_formatObject

Returns the value of attribute attr_internal_naming_format


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# File 'activesupport/lib/active_support/core_ext/module/attr_internal.rb', line 20

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 query methods.

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 'activesupport/lib/active_support/core_ext/module/aliasing.rb', line 62

def alias_attribute(new_name, old_name)
  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

#alias_method_chain(target, feature) {|aliased_target, punctuation| ... } ⇒ Object

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.

Yields:

  • (aliased_target, punctuation)

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# 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 = "#{aliased_target}_with_#{feature}#{punctuation}"
  without_method = "#{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?Boolean

A module may or may not have a name.

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

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

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"

Returns:

  • (Boolean)

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# File 'activesupport/lib/active_support/core_ext/module/anonymous.rb', line 16

def anonymous?
  name.nil?
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 '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) ⇒ Object

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


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# 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) ⇒ Object

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


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# 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) ⇒ Object

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

Options

  • :to - Specifies the target object

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

  • :allow_nil - if set to true, prevents a NoMethodError to be raised

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'

If the target is nil and does not respond to the delegated method a NoMethodError is raised, as with any other value. Sometimes, however, it makes sense to be robust to that situation and that is the purpose of the :allow_nil option: If the target is not nil, or it is and responds to the method, everything works as usual. But if it is nil and does not respond to the delegated method, nil is returned.

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

User.new.age # raises NoMethodError: undefined method `age'

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'

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# File 'activesupport/lib/active_support/core_ext/module/delegation.rb', line 141

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

  prefix, allow_nil = options.values_at(:prefix, :allow_nil)

  if prefix == true && to =~ /^[^a-z_]/
    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

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

  to = to.to_s
  to = 'self.class' if to == 'class'

  methods.each do |method|
    # Attribute writer methods only accept one argument. Makes sure []=
    # methods still accept two arguments.
    definition = (method =~ /[^\]]=$/) ? 'arg' : '*args, &block'

    # The following generated methods call 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
      module_eval(<<-EOS, file, line - 3)
        def #{method_prefix}#{method}(#{definition})        # def customer_name(*args, &block)
          _ = #{to}                                         #   _ = client
          if !_.nil? || nil.respond_to?(:#{method})         #   if !_.nil? || nil.respond_to?(:name)
            _.#{method}(#{definition})                      #     _.name(*args, &block)
          end                                               #   end
        end                                                 # end
      EOS
    else
      exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")

      module_eval(<<-EOS, file, line - 2)
        def #{method_prefix}#{method}(#{definition})                                          # def customer_name(*args, &block)
          _ = #{to}                                                                           #   _ = client
          _.#{method}(#{definition})                                                          #   _.name(*args, &block)
        rescue NoMethodError => e                                                             # rescue NoMethodError => e
          location = "%s:%d:in `%s'" % [__FILE__, __LINE__ - 2, '#{method_prefix}#{method}']  #   location = "%s:%d:in `%s'" % [__FILE__, __LINE__ - 2, 'customer_name']
          if _.nil? && e.backtrace.first == location                                          #   if _.nil? && e.backtrace.first == location
            #{exception}                                                                      #     # add helpful message to the exception
          else                                                                                #   else
            raise                                                                             #     raise
          end                                                                                 #   end
        end                                                                                   # end
      EOS
    end
  end
end

#deprecate(*method_names) ⇒ Object

deprecate :foo

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

You can also use custom deprecator instance:

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

Custom deprecators must respond to deprecation_warning(deprecated_method_name, message, caller_backtrace) method 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 'activesupport/lib/active_support/core_ext/module/deprecation.rb', line 22

def deprecate(*method_names)
  ActiveSupport::Deprecation.deprecate_methods(self, *method_names)
end

#local_constantsObject

:nodoc:


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# File 'activesupport/lib/active_support/core_ext/module/introspection.rb', line 59

def local_constants #:nodoc:
  constants(false)
end

#mattr_accessor(*syms) ⇒ Object

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"
end

AppConfiguration.google_api_key # => "123456789"
AppConfiguration.google_api_key = "overriding the api key!"
AppConfiguration.google_api_key # => "overriding the api key!"

To opt out of the instance writer method, pass instance_writer: false. To opt out of the instance reader method, pass instance_reader: false. To opt out of both instance methods, pass instance_accessor: false.


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# File 'activesupport/lib/active_support/core_ext/module/attribute_accessors.rb', line 62

def mattr_accessor(*syms)
  mattr_reader(*syms)
  mattr_writer(*syms)
end

#mattr_reader(*syms) ⇒ Object


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# 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|
    raise NameError.new('invalid attribute name') unless sym =~ /^[_A-Za-z]\w*$/
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      @@#{sym} = nil unless defined? @@#{sym}

      def self.#{sym}
        @@#{sym}
      end
    EOS

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

#mattr_writer(*syms) ⇒ Object


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

def mattr_writer(*syms)
  options = syms.extract_options!
  syms.each do |sym|
    raise NameError.new('invalid attribute name') unless sym =~ /^[_A-Za-z]\w*$/
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def self.#{sym}=(obj)
        @@#{sym} = obj
      end
    EOS

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

#methods_transplantable?Boolean

TODO: remove this after 1.9 support is dropped

Returns:

  • (Boolean)

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# File 'activesupport/lib/active_support/core_ext/module/method_transplanting.rb', line 4

def methods_transplantable? # :nodoc:
  x = Module.new { def foo; end }
  Module.new { define_method :bar, x.instance_method(:foo) }
  true
rescue TypeError
  false
end

#parentObject

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

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

def parent
  parent_name ? ActiveSupport::Inflector.constantize(parent_name) : Object
end

#parent_nameObject

Returns the name of the module containing this one.

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

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# File 'activesupport/lib/active_support/core_ext/module/introspection.rb', line 7

def parent_name
  if defined? @parent_name
    @parent_name
  else
    @parent_name = name =~ /::[^:]+\Z/ ? $`.freeze : nil
  end
end

#parentsObject

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]

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# File 'activesupport/lib/active_support/core_ext/module/introspection.rb', line 46

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

#qualified_const_defined?(path, search_parents = true) ⇒ Boolean

Returns:

  • (Boolean)

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

def qualified_const_defined?(path, search_parents=true)
  QualifiedConstUtils.raise_if_absolute(path)

  QualifiedConstUtils.names(path).inject(self) do |mod, name|
    return unless mod.const_defined?(name, search_parents)
    mod.const_get(name)
  end
  return true
end

#qualified_const_get(path) ⇒ Object


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# File 'activesupport/lib/active_support/core_ext/module/qualified_const.rb', line 36

def qualified_const_get(path)
  QualifiedConstUtils.raise_if_absolute(path)

  QualifiedConstUtils.names(path).inject(self) do |mod, name|
    mod.const_get(name)
  end
end

#qualified_const_set(path, value) ⇒ Object


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# File 'activesupport/lib/active_support/core_ext/module/qualified_const.rb', line 44

def qualified_const_set(path, value)
  QualifiedConstUtils.raise_if_absolute(path)

  const_name = path.demodulize
  mod_name = path.deconstantize
  mod = mod_name.empty? ? self : qualified_const_get(mod_name)
  mod.const_set(const_name, value)
end

#reachable?Boolean

:nodoc:

Returns:

  • (Boolean)

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# File 'activesupport/lib/active_support/core_ext/module/reachable.rb', line 5

def reachable? #:nodoc:
  !anonymous? && name.safe_constantize.equal?(self)
end

#redefine_method(method, &block) ⇒ Object


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# File 'activesupport/lib/active_support/core_ext/module/remove_method.rb', line 8

def redefine_method(method, &block)
  remove_possible_method(method)
  define_method(method, &block)
end

#remove_possible_method(method) ⇒ Object


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# 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)
    undef_method(method)
  end
end