Class: Class
Relationships & Source Files | |
Super Chains via Extension / Inclusion / Inheritance | |
Class Chain:
self,
::Module
|
|
Instance Chain:
self,
::Module
|
|
Inherits: | Module |
Defined in: | object.c, class.c |
Overview
Classes in Ruby are first-class objects—each is an instance of class Class
.
Typically, you create a new class by using:
class Name
# some code describing the class behavior
end
When a new class is created, an object of type Class
is initialized and assigned to a global constant (Name
in this case).
When Name.new
is called to create a new object, the .new method in Class
is run by default. This can be demonstrated by overriding .new in Class
:
class Class
alias old_new new
def new(*args)
print "Creating a new ", self.name, "\n"
old_new(*args)
end
end
class Name
end
n = Name.new
produces:
Creating a new Name
Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance, and the parentheses metaclasses. All metaclasses are instances of the class `Class'.
--------- +-...
| | |
BasicObject-----|-->(BasicObject)-------|-...
^ | ^ |
| | | |
Object---------|----->(Object)---------|-...
^ | ^ |
| | | |
------- | -------- |
| | | | | |
| Module-|---------|--->(Module)-|-...
| ^ | | ^ |
| | | | | |
| Class-|---------|---->(Class)-|-...
| ^ | | ^ |
| --- | ----
| |
obj--->OtherClass---------->(OtherClass)-----------...
Class Method Summary
-
.new(super_class = Object) ⇒ Class
constructor
Creates a new anonymous (unnamed) class with the given superclass (or ::Object if no parameter is given).
::Module - Inherited
.constants | In the first form, returns an array of the names of all constants accessible from the point of call. |
.nesting | Returns the list of |
.new | Creates a new anonymous module. |
Instance Attribute Summary
::Module - Inherited
#singleton_class? | Returns |
Instance Method Summary
-
#allocate ⇒ Object
Allocates space for a new object of class's class and does not call initialize on the new instance.
-
#new(args, ...) ⇒ Object
Calls #allocate to create a new object of class's class, then invokes that object's
initialize
method, passing it args. -
#superclass ⇒ Class?
Returns the superclass of class, or
nil
. -
#inherited(subclass)
private
Callback invoked whenever a subclass of the current class is created.
::Module - Inherited
#< | Returns true if mod is a subclass of other. |
#<= | Returns true if mod is a subclass of other or is the same as other. |
#<=> | Comparison—Returns -1, 0, +1 or nil depending on whether |
#== | Alias for Object#eql?. |
#=== | Case Equality—Returns |
#> | Returns true if mod is an ancestor of other. |
#>= | Returns true if mod is an ancestor of other, or the two modules are the same. |
#ancestors | Returns a list of modules included/prepended in mod (including mod itself). |
#autoload | 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. |
#autoload? | Returns filename to be loaded if name is registered as |
#class_eval | Evaluates the string or block in the context of mod, except that when a block is given, constant/class variable lookup is not affected. |
#class_exec | Evaluates the given block in the context of the class/module. |
#class_variable_defined? | Returns |
#class_variable_get | Returns the value of the given class variable (or throws a ::NameError exception). |
#class_variable_set | Sets the class variable named by symbol to the given object. |
#class_variables | Returns an array of the names of class variables in mod. |
#const_defined? | Says whether mod or its ancestors have a constant with the given name: |
#const_get | Checks for a constant with the given name in mod. |
#const_missing | Invoked when a reference is made to an undefined constant in mod. |
#const_set | Sets the named constant to the given object, returning that object. |
#constants | Returns an array of the names of the constants accessible in mod. |
#deprecate_constant, | |
#freeze | Prevents further modifications to mod. |
#include | Invokes Module#append_features on each parameter in reverse order. |
#include? | Returns |
#included_modules | Returns the list of modules included in mod. |
#inspect | Alias for Module#to_s. |
#instance_method | Returns an ::UnboundMethod representing the given instance method in mod. |
#instance_methods | Returns an array containing the names of the public and protected instance methods in the receiver. |
#method_defined? | Returns |
#module_eval | Alias for Module#class_eval. |
#module_exec | Alias for Module#class_exec. |
#name | Returns the name of the module mod. |
#prepend | Invokes Module#prepend_features on each parameter in reverse order. |
#private_class_method | Makes existing class methods private. |
#private_constant | Makes a list of existing constants private. |
#private_instance_methods | Returns a list of the private instance methods defined in mod. |
#private_method_defined? | Returns |
#protected_instance_methods | Returns a list of the protected instance methods defined in mod. |
#protected_method_defined? | Returns |
#public_class_method | Makes a list of existing class methods public. |
#public_constant | Makes a list of existing constants public. |
#public_instance_method | Similar to instance_method, searches public method only. |
#public_instance_methods | Returns a list of the public instance methods defined in mod. |
#public_method_defined? | Returns |
#remove_class_variable | Removes the definition of the sym, returning that constant's value. |
#to_s | Returns a string representing this module or class. |
#alias_method | Makes new_name a new copy of the method old_name. |
#append_features | When this module is included in another, Ruby calls |
#attr, | |
#attr_accessor | Defines a named attribute for this module, where the name is symbol. |
#attr_reader | Creates instance variables and corresponding methods that return the value of each instance variable. |
#attr_writer | Creates an accessor method to allow assignment to the attribute symbol |
#define_method | Defines an instance method in the receiver. |
#extend_object | Extends the specified object by adding this module's constants and methods (which are added as singleton methods). |
#extended | The equivalent of |
#included | Callback invoked whenever the receiver is included in another module or class. |
#method_added | Invoked as a callback whenever an instance method is added to the receiver. |
#method_removed | Invoked as a callback whenever an instance method is removed from the receiver. |
#method_undefined, | |
#module_function | Creates module functions for the named methods. |
#prepend_features | When this module is prepended in another, Ruby calls |
#prepended | The equivalent of |
#private | With no arguments, sets the default visibility for subsequently defined methods to private. |
#protected | With no arguments, sets the default visibility for subsequently defined methods to protected. |
#public | With no arguments, sets the default visibility for subsequently defined methods to public. |
#refine | Refine klass in the receiver. |
#remove_const | Removes the definition of the given constant, returning that constant's previous value. |
#remove_method | Removes the method identified by symbol from the current class. |
#undef_method | Prevents the current class from responding to calls to the named method. |
#using | Import class refinements from module into the current class or module definition. |
Constructor Details
.new(super_class = Object) ⇒ Class
.new(super_class = Object) {|mod| ... } ⇒ Class
Class
.new(super_class = Object) {|mod| ... } ⇒ Class
Creates a new anonymous (unnamed) class with the given superclass (or ::Object if no parameter is given). You can give a class a name by assigning the class object to a constant.
If a block is given, it is passed the class object, and the block is evaluated in the context of this class using class_eval
.
fred = Class.new do
def meth1
"hello"
end
def meth2
"bye"
end
end
a = fred.new #=> #<#<Class:0x100381890>:0x100376b98>
a.meth1 #=> "hello"
a.meth2 #=> "bye"
Assign the class to a constant (name starting uppercase) if you want to treat it like a regular class.
Instance Method Details
#allocate ⇒ Object
Allocates space for a new object of class's class and does not call initialize on the new instance. The returned object must be an instance of class.
klass = Class.new do
def initialize(*args)
@initialized = true
end
def initialized?
@initialized || false
end
end
klass.allocate.initialized? #=> false
#inherited(subclass) (private)
Callback invoked whenever a subclass of the current class is created.
Example:
class Foo
def self.inherited(subclass)
puts "New subclass: #{subclass}"
end
end
class Bar < Foo
end
class Baz < Bar
end
produces:
New subclass: Bar
New subclass: Baz
#new(args, ...) ⇒ Object
#superclass ⇒ Class
?
Returns the superclass of class, or nil
.
File.superclass #=> IO
IO.superclass #=> Object
Object.superclass #=> BasicObject
class Foo; end
class Bar < Foo; end
Bar.superclass #=> Foo
Returns nil when the given class does not have a parent class:
BasicObject.superclass #=> nil