Class: Module

Returns the list of Modules nested at the point of call.

module M1
  module M2
    $a = Module.nesting
  end
end
$a           #=> [M1::M2, M1]
$a[0].name   #=> "M1::M2"

Returns true if mod is a subclass of other or is the same as other. Returns nil if there's no relationship between the two. (Think of the relationship in terms of the class definition: “class A<B” implies “A<B”.)

Comparison—Returns -1, 0, +1 or nil depending on whether module includes other_module, they are the same, or if module is included by other_module.

Returns nil if module has no relationship with other_module, if other_module is not a module, or if the two values are incomparable.

Alias for Object#eql?. Equality — At the ::Object level, == returns true only if obj and other are the same object. Typically, this method is overridden in descendant classes to provide class-specific meaning.

Unlike ==, the equal? method should never be overridden by subclasses as it is used to determine object identity (that is, a.equal?(b) if and only if a is the same object as b):

obj = "a"
other = obj.dup

obj == other      #=> true
obj.equal? other  #=> false
obj.equal? obj    #=> true

The eql? method returns true if obj and other refer to the same hash key. This is used by ::Hash to test members for equality. For objects of class ::Object, eql? is synonymous with ==. Subclasses normally continue this tradition by aliasing eql? to their overridden == method, but there are exceptions. ::Numeric types, for example, perform type conversion across ==, but not across eql?, so:

1 == 1.0     #=> true
1.eql? 1.0   #=> false

Case Equality—Returns true if obj is an instance of mod or and instance of one of mod's descendants. Of limited use for modules, but can be used in case statements to classify objects by class.

Returns true if mod is an ancestor of other. Returns nil if there's no relationship between the two. (Think of the relationship in terms of the class definition: “class A<B” implies “B>A”.)

Returns true if mod is an ancestor of other, or the two modules are the same. Returns nil if there's no relationship between the two. (Think of the relationship in terms of the class definition: “class A<B” implies “B>A”.)

Makes new_name a new copy of the method old_name. This can be used to retain access to methods that are overridden.

module Mod
  alias_method :orig_exit, :exit
  def exit(code=0)
    puts "Exiting with code #{code}"
    orig_exit(code)
  end
end
include Mod
exit(99)

produces:

Exiting with code 99

Returns a list of modules included/prepended in mod (including mod itself).

module Mod
  include Math
  include Comparable
  prepend Enumerable
end

Mod.ancestors        #=> [Enumerable, Mod, Comparable, Math]
Math.ancestors       #=> [Math]
Enumerable.ancestors #=> [Enumerable]

When this module is included in another, Ruby calls append_features in this module, passing it the receiving module in mod. Ruby's default implementation is to add the constants, methods, and module variables of this module to mod if this module has not already been added to mod or one of its ancestors. See also #include.

Defines a named attribute for this module, where the name is symbol.id2name, creating an instance variable (@name) and a corresponding access method to read it. Also creates a method called name= to set the attribute. ::String arguments are converted to symbols.

module Mod
  attr_accessor(:one, :two)
end
Mod.instance_methods.sort   #=> [:one, :one=, :two, :two=]

Creates instance variables and corresponding methods that return the value of each instance variable. Equivalent to calling “attr:name'' on each name in turn. ::String arguments are converted to symbols.

Creates an accessor method to allow assignment to the attribute symbol.id2name. ::String arguments are converted to symbols.

Registers filename to be loaded (using Kernel.require) the first time that module (which may be a ::String or a symbol) is accessed in the namespace of mod.

module A
end
A.autoload(:B, "b")
A::B.doit            # autoloads "b"

Returns filename to be loaded if name is registered as #autoload in the namespace of mod.

module A
end
A.autoload(:B, "b")
A.autoload?(:B)            #=> "b"

Evaluates the string or block in the context of mod, except that when a block is given, constant/class variable lookup is not affected. This can be used to add methods to a class. #module_eval returns the result of evaluating its argument. The optional filename and lineno parameters set the text for error messages.

class Thing
end
a = %q{def hello() "Hello there!" end}
Thing.module_eval(a)
puts Thing.new.hello()
Thing.module_eval("invalid code", "dummy", 123)

produces:

Hello there!
dummy:123:in `module_eval': undefined local variable
    or method `code' for Thing:Class

Evaluates the given block in the context of the class/module. The method defined in the block will belong to the receiver. Any arguments passed to the method will be passed to the block. This can be used if the block needs to access instance variables.

class Thing
end
Thing.class_exec{
  def hello() "Hello there!" end
}
puts Thing.new.hello()

produces:

Hello there!

Returns true if the given class variable is defined in obj. ::String arguments are converted to symbols.

class Fred
  @@foo = 99
end
Fred.class_variable_defined?(:@@foo)    #=> true
Fred.class_variable_defined?(:@@bar)    #=> false

Returns the value of the given class variable (or throws a ::NameError exception). The @@ part of the variable name should be included for regular class variables. ::String arguments are converted to symbols.

class Fred
  @@foo = 99
end
Fred.class_variable_get(:@@foo)     #=> 99

Sets the class variable named by symbol to the given object. If the class variable name is passed as a string, that string is converted to a symbol.

class Fred
  @@foo = 99
  def foo
    @@foo
  end
end
Fred.class_variable_set(:@@foo, 101)     #=> 101
Fred.new.foo                             #=> 101

Returns an array of the names of class variables in mod. This includes the names of class variables in any included modules, unless the inherit parameter is set to false.

class One
  @@var1 = 1
end
class Two < One
  @@var2 = 2
end
One.class_variables          #=> [:@@var1]
Two.class_variables          #=> [:@@var2, :@@var1]
Two.class_variables(false)   #=> [:@@var2]

Says whether mod or its ancestors have a constant with the given name:

Float.const_defined?(:EPSILON)      #=> true, found in Float itself
Float.const_defined?("String")      #=> true, found in Object (ancestor)
BasicObject.const_defined?(:Hash)   #=> false

If mod is a Module, additionally ::Object and its ancestors are checked:

Math.const_defined?(:String)   #=> true, found in Object

In each of the checked classes or modules, if the constant is not present but there is an autoload for it, true is returned directly without autoloading:

module Admin
  autoload :User, 'admin/user'
end
Admin.const_defined?(:User)   #=> true

If the constant is not found the callback #const_missing is not called and the method returns false.

If inherit is false, the lookup only checks the constants in the receiver:

IO.const_defined?(:SYNC)          #=> true, found in File::Constants (ancestor)
IO.const_defined?(:SYNC, false)   #=> false, not found in IO itself

In this case, the same logic for autoloading applies.

If the argument is not a valid constant name a ::NameError is raised with the message “wrong constant name name”:

Hash.const_defined? 'foobar'   #=> NameError: wrong constant name foobar

Checks for a constant with the given name in mod. If inherit is set, the lookup will also search the ancestors (and ::Object if mod is a Module).

The value of the constant is returned if a definition is found, otherwise a ::NameError is raised.

Math.const_get(:PI)   #=> 3.14159265358979

This method will recursively look up constant names if a namespaced class name is provided. For example:

module Foo; class Bar; end end
Object.const_get 'Foo::Bar'

The inherit flag is respected on each lookup. For example:

module Foo
  class Bar
    VAL = 10
  end

  class Baz < Bar; end
end

Object.const_get 'Foo::Baz::VAL'         # => 10
Object.const_get 'Foo::Baz::VAL', false  # => NameError

If the argument is not a valid constant name a ::NameError will be raised with a warning “wrong constant name”.

Object.const_get 'foobar' #=> NameError: wrong constant name foobar

Invoked when a reference is made to an undefined constant in mod. It is passed a symbol for the undefined constant, and returns a value to be used for that constant. The following code is an example of the same:

def Foo.const_missing(name)
  name # return the constant name as Symbol
end

Foo::UNDEFINED_CONST    #=> :UNDEFINED_CONST: symbol returned

In the next example when a reference is made to an undefined constant, it attempts to load a file whose name is the lowercase version of the constant (thus class Fred is assumed to be in file fred.rb). If found, it returns the loaded class. It therefore implements an autoload feature similar to Kernel.autoload and #autoload.

def Object.const_missing(name)
  @looked_for ||= {}
  str_name = name.to_s
  raise "Class not found: #{name}" if @looked_for[str_name]
  @looked_for[str_name] = 1
  file = str_name.downcase
  require file
  klass = const_get(name)
  return klass if klass
  raise "Class not found: #{name}"
end

Sets the named constant to the given object, returning that object. Creates a new constant if no constant with the given name previously existed.

Math.const_set("HIGH_SCHOOL_PI", 22.0/7.0)   #=> 3.14285714285714
Math::HIGH_SCHOOL_PI - Math::PI              #=> 0.00126448926734968

If sym or str is not a valid constant name a ::NameError will be raised with a warning “wrong constant name”.

Object.const_set('foobar', 42) #=> NameError: wrong constant name foobar

Returns an array of the names of the constants accessible in mod. This includes the names of constants in any included modules (example at start of section), unless the inherit parameter is set to false.

The implementation makes no guarantees about the order in which the constants are yielded.

IO.constants.include?(:SYNC)        #=> true
IO.constants(false).include?(:SYNC) #=> false

Also see #const_defined?.

Defines an instance method in the receiver. The method parameter can be a ::Proc, a ::Method or an ::UnboundMethod object. If a block is specified, it is used as the method body. This block is evaluated using instance_eval, a point that is tricky to demonstrate because define_method is private. (This is why we resort to the send hack in this example.)

class A
  def fred
    puts "In Fred"
  end
  def create_method(name, &block)
    self.class.send(:define_method, name, &block)
  end
  define_method(:wilma) { puts "Charge it!" }
end
class B < A
  define_method(:barney, instance_method(:fred))
end
a = B.new
a.barney
a.wilma
a.create_method(:betty) { p self }
a.betty

produces:

In Fred
Charge it!
#<B:0x401b39e8>

Extends the specified object by adding this module's constants and methods (which are added as singleton methods). This is the callback method used by Object#extend.

module Picky
  def Picky.extend_object(o)
    if String === o
      puts "Can't add Picky to a String"
    else
      puts "Picky added to #{o.class}"
      super
    end
  end
end
(s = Array.new).extend Picky  # Call Object.extend
(s = "quick brown fox").extend Picky

produces:

Picky added to Array
Can't add Picky to a String

The equivalent of #included, but for extended modules.

module A
  def self.extended(mod)
    puts "#{self} extended in #{mod}"
  end
end
module Enumerable
  extend A
end
 # => prints "A extended in Enumerable"

Prevents further modifications to mod.

This method returns self.

Invokes #append_features on each parameter in reverse order.

Returns true if module is included in mod or one of mod's ancestors.

module A
end
class B
  include A
end
class C < B
end
B.include?(A)   #=> true
C.include?(A)   #=> true
A.include?(A)   #=> false

Callback invoked whenever the receiver is included in another module or class. This should be used in preference to #append_features if your code wants to perform some action when a module is included in another.

module A
  def A.included(mod)
    puts "#{self} included in #{mod}"
  end
end
module Enumerable
  include A
end
 # => prints "A included in Enumerable"

Returns the list of modules included in mod.

module Mixin
end

module Outer
  include Mixin
end

Mixin.included_modules   #=> []
Outer.included_modules   #=> [Mixin]

Alias for #to_s.

Returns an ::UnboundMethod representing the given instance method in mod.

class Interpreter
  def do_a() print "there, "; end
  def do_d() print "Hello ";  end
  def do_e() print "!\n";     end
  def do_v() print "Dave";    end
  Dispatcher = {
    "a" => instance_method(:do_a),
    "d" => instance_method(:do_d),
    "e" => instance_method(:do_e),
    "v" => instance_method(:do_v)
  }
  def interpret(string)
    string.each_char {|b| Dispatcher[b].bind(self).call }
  end
end

interpreter = Interpreter.new
interpreter.interpret('dave')

produces:

Hello there, Dave!

Returns an array containing the names of the public and protected instance methods in the receiver. For a module, these are the public and protected methods; for a class, they are the instance (not singleton) methods. If the optional parameter is false, the methods of any ancestors are not included.

module A
  def method1()  end
end
class B
  include A
  def method2()  end
end
class C < B
  def method3()  end
end

A.instance_methods(false)                   #=> [:method1]
B.instance_methods(false)                   #=> [:method2]
B.instance_methods(true).include?(:method1) #=> true
C.instance_methods(false)                   #=> [:method3]
C.instance_methods.include?(:method2)       #=> true

Invoked as a callback whenever an instance method is added to the receiver.

module Chatty
  def self.method_added(method_name)
    puts "Adding #{method_name.inspect}"
  end
  def self.some_class_method() end
  def some_instance_method() end
end

produces:

Adding :some_instance_method

Returns true if the named method is defined by mod (or its included modules and, if mod is a class, its ancestors). Public and protected methods are matched. ::String arguments are converted to symbols.

module A
  def method1()  end
  def protected_method1()  end
  protected :protected_method1
end
class B
  def method2()  end
  def private_method2()  end
  private :private_method2
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1              #=> true
C.method_defined? "method1"             #=> true
C.method_defined? "method2"             #=> true
C.method_defined? "method3"             #=> true
C.method_defined? "protected_method1"   #=> true
C.method_defined? "method4"             #=> false
C.method_defined? "private_method2"     #=> false

Invoked as a callback whenever an instance method is removed from the receiver.

module Chatty
  def self.method_removed(method_name)
    puts "Removing #{method_name.inspect}"
  end
  def self.some_class_method() end
  def some_instance_method() end
  class << self
    remove_method :some_class_method
  end
  remove_method :some_instance_method
end

produces:

Removing :some_instance_method

Alias for #class_eval.

Alias for #class_exec.

Creates module functions for the named methods. These functions may be called with the module as a receiver, and also become available as instance methods to classes that mix in the module. Module functions are copies of the original, and so may be changed independently. The instance-method versions are made private. If used with no arguments, subsequently defined methods become module functions. ::String arguments are converted to symbols.

module Mod
  def one
    "This is one"
  end
  module_function :one
end
class Cls
  include Mod
  def call_one
    one
  end
end
Mod.one     #=> "This is one"
c = Cls.new
c.call_one  #=> "This is one"
module Mod
  def one
    "This is the new one"
  end
end
Mod.one     #=> "This is one"
c.call_one  #=> "This is the new one"

Returns the name of the module mod. Returns nil for anonymous modules.

Invokes #prepend_features on each parameter in reverse order.

When this module is prepended in another, Ruby calls prepend_features in this module, passing it the receiving module in mod. Ruby's default implementation is to overlay the constants, methods, and module variables of this module to mod if this module has not already been added to mod or one of its ancestors. See also #prepend.

The equivalent of #included, but for prepended modules.

module A
  def self.prepended(mod)
    puts "#{self} prepended to #{mod}"
  end
end
module Enumerable
  prepend A
end
 # => prints "A prepended to Enumerable"

With no arguments, sets the default visibility for subsequently defined methods to private. With arguments, sets the named methods to have private visibility. ::String arguments are converted to symbols.

module Mod
  def a()  end
  def b()  end
  private
  def c()  end
  private :a
end
Mod.private_instance_methods   #=> [:a, :c]

Makes existing class methods private. Often used to hide the default constructor .new.

::String arguments are converted to symbols.

class SimpleSingleton  # Not thread safe
  private_class_method :new
  def SimpleSingleton.create(*args, &block)
    @me = new(*args, &block) if ! @me
    @me
  end
end

Makes a list of existing constants private.

Returns a list of the private instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

module Mod
  def method1()  end
  private :method1
  def method2()  end
end
Mod.instance_methods           #=> [:method2]
Mod.private_instance_methods   #=> [:method1]

Returns true if the named private method is defined by _ mod_ (or its included modules and, if mod is a class, its ancestors). ::String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  private
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1            #=> true
C.private_method_defined? "method1"   #=> false
C.private_method_defined? "method2"   #=> true
C.method_defined? "method2"           #=> false

With no arguments, sets the default visibility for subsequently defined methods to protected. With arguments, sets the named methods to have protected visibility. ::String arguments are converted to symbols.

Returns a list of the protected instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

Returns true if the named protected method is defined by mod (or its included modules and, if mod is a class, its ancestors). ::String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  protected
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1              #=> true
C.protected_method_defined? "method1"   #=> false
C.protected_method_defined? "method2"   #=> true
C.method_defined? "method2"             #=> true

With no arguments, sets the default visibility for subsequently defined methods to public. With arguments, sets the named methods to have public visibility. ::String arguments are converted to symbols.

Makes a list of existing class methods public.

::String arguments are converted to symbols.

Makes a list of existing constants public.

Similar to instance_method, searches public method only.

Returns a list of the public instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

Returns true if the named public method is defined by mod (or its included modules and, if mod is a class, its ancestors). ::String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  protected
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1           #=> true
C.public_method_defined? "method1"   #=> true
C.public_method_defined? "method2"   #=> false
C.method_defined? "method2"          #=> true

Refine klass in the receiver.

Returns an overlaid module.

Removes the definition of the sym, returning that constant's value.

class Dummy
  @@var = 99
  puts @@var
  remove_class_variable(:@@var)
  p(defined? @@var)
end

produces:

99
nil

Removes the definition of the given constant, returning that constant's previous value. If that constant referred to a module, this will not change that module's name and can lead to confusion.

Removes the method identified by symbol from the current class. For an example, see #undef_method. ::String arguments are converted to symbols.

Returns a string representing this module or class. For basic classes and modules, this is the name. For singletons, we show information on the thing we're attached to as well.

Prevents the current class from responding to calls to the named method. Contrast this with #remove_method, which deletes the method from the particular class; Ruby will still search superclasses and mixed-in modules for a possible receiver. ::String arguments are converted to symbols.

class Parent
  def hello
    puts "In parent"
  end
end
class Child < Parent
  def hello
    puts "In child"
  end
end

c = Child.new
c.hello

class Child
  remove_method :hello  # remove from child, still in parent
end
c.hello

class Child
  undef_method :hello   # prevent any calls to 'hello'
end
c.hello

produces:

In child
In parent
prog.rb:23: undefined method `hello' for #<Child:0x401b3bb4> (NoMethodError)

Import class refinements from module into the current class or module definition.