Inheritance/Single

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Task
Inheritance/Single
You are encouraged to solve this task according to the task description, using any language you may know.
This task is about derived types; for implementation inheritance, see Polymorphism.

Inheritance is an operation of type algebra that creates a new type from one or several parent types. The obtained type is called derived type. It inherits some of the properties of its parent types. Usually inherited properties are:

  • methods
  • components
  • parts of the representation

The class of the new type is a subclass of the classes rooted in the parent types. When all (in certain sense) properties of the parents are preserved by the derived type, it is said to be a Liskov subtype. When properties are preserved then the derived type is substitutable for its parents in all contexts. Usually full substitutability is achievable only in some contexts.

Inheritance is

  • single, when only one parent is allowed
  • multiple, otherwise

Some single inheritance languages usually allow multiple inheritance for certain abstract types, interfaces in particular.

Inheritance can be considered as a relation parent-child. Parent types are sometimes called supertype, the derived ones are subtype. This relation is transitive and reflexive. Types bound by the relation form a wp:Directed_acyclic_graph directed acyclic graph (ignoring reflexivity). With single inheritance it becomes a tree.

Task: Show a tree of types which inherit from each other. The top of the tree should be a class called Animal. The second level should have Dog and Cat. Under Dog should be Lab and Collie. None of the classes need to have any functions, the only thing they need to do is inherit from the specified superclasses (overriding functions should be shown in Polymorphism). The tree should look like this: 

    Animal
      /\
     /  \
    /    \
   Dog   Cat
   /\
  /  \
 /    \
Lab   Collie

Contents

[edit] ActionScript

public class Animal {
    // ...
}
public class Cat extends Animal {
    // ...
}
public class Dog extends Animal {
    // ...
}
public class Lab extends Dog {
    // ...
}
public class Collie extends Dog {
    // ...
}

[edit] Ada

package Inheritance is
   type Animal is tagged private;
   type Dog is new Animal with private;
   type Cat is new Animal with private;
   type Lab is new Dog with private;
   type Collie is new Dog with private;
private
   type Animal is tagged null record;
   type Dog is new Animal with null record;
   type Cat is new Animal with null record;
   type Lab is new Dog with null record;
   type Collie is new Dog with null record;
end Inheritance;

[edit] Aikido

class Animal{
   //functions go here...
}
class Dog extends Animal {
   //functions go here...
}
class Cat extends Animal {
   //functions go here...
}
class Lab extends Dog {
   //functions go here...
}
class Collie extends Dog {
   //functions go here...
}

[edit] AutoHotkey

Works with: AutoHotkey_L

AutoHotkey_L is prototype-based. However, for convenience, class-syntax may be used to create a base object. 

dog := new Collie
MsgBox, % "A " dog.__Class " is a " dog.base.base.__Class " and is part of the " dog.kingdom " kingdom."
 
class Animal {
   static kingdom := "Animalia" ; Class variable
}
class Dog extends Animal {
}
class Cat extends Animal {
}
class Lab extends Dog {
}
class Collie extends Dog {
}

[edit] BBC BASIC

Works with: BBC BASIC for Windows
      INSTALL @lib$+"CLASSLIB"
 
      DIM Animal{method}
      PROC_class(Animal{})
 
      DIM Cat{method}
      PROC_inherit(Cat{}, Animal{})
      PROC_class(Cat{})
 
      DIM Dog{method}
      PROC_inherit(Dog{}, Animal{})
      PROC_class(Dog{})
 
      DIM Labrador{method}
      PROC_inherit(Labrador{}, Dog{})
      PROC_class(Labrador{})
 
      DIM Collie{method}
      PROC_inherit(Collie{}, Dog{})
      PROC_class(Collie{})

[edit] C

[edit] C++

class Animal
{
  // ... 
};
 
class Dog: public Animal
{
  // ... 
};
 
class Lab: public Dog
{
  // ...
};
 
class Collie: public Dog
{
  // ...
};
 
class Cat: public Animal
{
  // ...
};

[edit] Clojure

This is not very useful in clojure 

(gen-class :name Animal)
(gen-class :name Dog :extends Animal)
(gen-class :name Cat :extends Animal)
(gen-class :name Lab :extends Dog)
(gen-class :name Collie :extends Dog)

More useful: 

(derive ::dog ::animal)
(derive ::cat ::animal)
(derive ::lab ::dog)
(derive ::collie ::dog)

use: 

user> (isa? ::dog ::animal)
true
user> (isa? ::dog ::cat)
false
user> (isa? ::collie ::animal)
true

[edit] Common Lisp

Using CLOS classes, we have the following: 

(defclass animal ()       ())
(defclass dog    (animal) ())
(defclass lab    (dog)    ())
(defclass collie (dog)    ())
(defclass cat    (animal) ())

Alternatively, since there is no multiple inheritance in the task requirement, structures could also be used: 

(defstruct animal)
(defstruct (dog    (:include animal)))
(defstruct (lab    (:include dog)))
(defstruct (collie (:include dog)))
(defstruct (cat    (:include animal)))

(Structures are less flexible than CLOS objects but often somewhat more efficiently implemented, due to those restrictions.)

Inheritance is not required for object-oriented programming in Lisp. It is used for code reuse, because it allows common utilities and protocol conventions to be factored out into base class methods. However, a class doesn't have to inherit from a base class just so that some existing methods can work with instances of that class.

Furthermore, all of the "basic types" also have a class, so methods can be readily specialized to lists, integers, strings, symbols, et cetera. This is done without having to modify any class definitions. 

 
;;; ASN.1 serialization logic specialized for animal class
(defmethod serialize-to-asn-1 ((a animal))
  #| ... |#
  )
 
 ;;; casually introduce the method over strings too; no relation to animal
(defmethod serialize-to-asn-1 ((s string))
  #| ... #|
  )

These classes do not have to inherit from some interface or base class which provides a prototype for the serialize-to-asn-1 method. Such a requirement has more to do with static typing than object oriented programming. Usually in languages which require such inheritance, there are also statically typed references. A class must conform to some "ASNEncodable" class so that its instances can be passed to functions which expect references to an ASN1Encodable type, which is verified at compile time.

[edit] Component Pascal 

 
	TYPE
		Animal = ABSTRACT RECORD (*  *) END;
		Cat = RECORD (Animal)  (*  *) END; (* final record (cannot be extended) - by default *)
		Dog = EXTENSIBLE RECORD (Animal)  (*  *) END; (* extensible record *)
		Lab = RECORD (Dog)  (*  *) END;
		Collie = RECORD (Dog)  (*  *) END;
 

[edit] C#

class Animal
{ /* ... */ }
 
class Dog : Animal
{ /* ... */ }
 
class Lab : Dog
{ /* ... */ }
 
class Collie : Dog
{ /* ... */ }
 
class Cat : Animal
{ /* ... */ }

[edit] D

class Animal {
    // ...
}
 
class Dog: Animal {
    // ...
}
 
class Lab: Dog {
    // ...
}
 
class Collie: Dog {
    // ...
}
 
class Cat: Animal {
    // ...
}
 
void main() {}

[edit] Delphi

type
  Animal = class(TObject)
  private
    // private functions/variables
  public
    // public functions/variables
  end;
 
  Dog = class(Animal);
  Cat = class(Animal);
  Collie = class(Dog);
  Lab = class(Dog);

[edit] DWScript

type
  Animal = class(TObject)
  private
    // private functions/variables
  public
    // public functions/variables
  end;
 
type Dog = class(Animal) end;
type Cat = class(Animal) end;
type Collie = class(Dog) end;
type Lab = class(Dog) end;

[edit] E

Outside of interactions with the host platform's objects, E does not generally deal in complex type hierarchies; the focus is more on "what guarantees does this object provide", and composition rather than inheritance. However, it is possible to set up a type hierarchy scheme with just a bit of code.

In E, a guard accepts, or coerces, certain objects and rejects others; its range constitutes a type. An auditor examines the implementation of an object and marks it approved; a stamp is an auditor which does no actual checking. Here, we create a guard/stamp pair; the guard accepts every stamped object. The stamp also asks for each supertype's stamp on the objects it audits. 

def makeType(label, superstamps) {
    def stamp {
        to audit(audition) {
            for s in superstamps { audition.ask(s) }
            return true
        }
    }
    def guard {
        to coerce(specimen, ejector) {
            if (__auditedBy(stamp, specimen)) {
                return specimen
            } else {
                throw.eject(ejector, `$specimen is not a $label`)
            }
        }
    }
    return [guard, stamp]
}

Setting up the task's specified tree: 

def [Animal, AnimalStamp] := makeType("Animal", [])
 
def [Cat, CatStamp] := makeType("Cat", [AnimalStamp])
def [Dog, DogStamp] := makeType("Dog", [AnimalStamp])
 
def [Lab, LabStamp] := makeType("Lab", [DogStamp])
def [Collie, CollieStamp] := makeType("Collie", [DogStamp])

Some example objects: 

def fido implements LabStamp {}
def tom implements CatStamp {}
def brick {} # not an animal

Testing against the types: 

? fido :Animal
# value: <fido>
 
? fido :Cat
# problem: <fido> is not a Cat
 
? fido :Lab
# value: <fido>
 
? tom :Animal
# value: <tom>
 
? tom :Cat
# value: <tom>
 
? brick :Animal
# problem: <brick> is not a Animal

[edit] Eiffel

class
    ANIMAL
end
class
    DOG
inherit
    ANIMAL
end
class
    CAT
inherit
    ANIMAL
end
class
    LAB
inherit
    DOG
end
class
    COLLIE
inherit
    DOG
end

[edit] Factor

TUPLE: animal ;
TUPLE: dog < animal ;
TUPLE: cat < animal ;
TUPLE: lab < dog ;
TUPLE: collie < dog ;

[edit] Fancy

 
class Animal {
  # ...
}
 
class Dog : Animal {
  # ...
}
 
class Cat : Animal {
  # ...
}
 
class Lab : Dog {
  # ...
}
 
class Collie : Dog {
  # ...
}
 

[edit] Fantom

 
class Animal 
{
}
 
class Dog : Animal 
{
}
 
class Cat : Animal 
{
}
 
class Lab : Dog 
{
}
 
class Collie : Dog 
{
}
 

[edit] Forth

Works with: 4tH version 3.61.5

There are numerous, mutually incompatible object oriented frameworks for Forth. This one works with the FOOS preprocessor extension of 4tH. 

include 4pp/lib/foos.4pp
 
:: Animal class end-class {} ;
:: Dog extends    Animal end-extends {} ;
:: Cat extends    Animal end-extends {} ;
:: Lab extends    Dog    end-extends {} ;
:: Collie extends Dog    end-extends {} ;

[edit] Fortran

OO has been part of the Fortran standard since 2003 but the compilers are still playing catchup. This example builds with the Intel 11.1.069 compiler (free for personal use on linux). 

 
module anim
 
  type animal
  end type animal
 
  type, extends(animal) :: dog
  end type dog
 
  type, extends(animal) :: cat
  end type cat
 
  type, extends(dog) :: lab
  end type lab
 
  type, extends(dog) :: collie
  end type collie
 
end module anim
 


[edit] F#

The () behind the class names indicates a public default constructor; you need some type of public constructor to derive from a class. 

type Animal() =
  class  // explicit syntax needed for empty class
  end
 
type Dog() =
  inherit Animal()
 
type Lab() =
  inherit Dog()
 
type Collie() =
  inherit Dog()
 
type Cat() =
  inherit Animal()

[edit] Go

Go eschews most trappings of inheritance, yet it's anonymous field feature allows building one struct type upon another and accessing fields of "embedded" types without extra synax. 

package main
 
type animal struct {
    alive bool
}
 
type dog struct {
    animal
    obedienceTrained bool
}
 
type cat struct {
    animal
    litterBoxTrained bool
}
 
type lab struct {
    dog
    color string
}
 
type collie struct {
    dog
    catchesFrisbee bool
}
 
func main() {
    var pet lab
    pet.alive = true
    pet.obedienceTrained = false
    pet.color = "yellow"
}
 

[edit] Groovy

class Animal{
   //contents go here...
}
class Dog extends Animal{
   //contents go here...
}
class Cat extends Animal{
   //contents go here...
}
class Lab extends Dog{
   //contents go here...
}
class Collie extends Dog{
   //contents go here...
}

[edit] Haskell

A type can't inherit properties from other types, but it can belong to any number of type classes, which may themselves be subclasses of other type classes. 

class Animal a
class Animal a => Cat a
class Animal a => Dog a
class Dog a => Lab a
class Dog a => Collie a

[edit] Haxe

class Animal {
    // ...
}
class Cat extends Animal {
    // ...
}
class Dog extends Animal {
    // ...
}
class Lab extends Dog {
    // ...
}
class Collie extends Dog {
    // ...
}

[edit] Icon and Unicon

This example only works in Unicon. 

 
class Animal ()
end
 
class Dog : Animal  ()
end
 
class Cat : Animal  ()
end
 
class Lab : Dog  ()
end
 
class Collie : Dog ()
end
 

[edit] Inform 7

An animal is a kind of thing.
A cat is a kind of animal.
A dog is a kind of animal.
A collie is a kind of dog.
A lab is a kind of dog.

"Animal" is actually a predefined kind in Inform 7, so its definition here is redundant (but legal).

[edit] Io

Animal := Object clone
Cat := Animal clone
Dog := Animal clone
Collie := Dog clone
Lab := Dog clone

[edit] J

Here is how this would normally be done: 

coclass 'Animal'
coclass 'Dog'
coinsert 'Animal'
coclass 'Cat'
coinsert 'Animal'
coclass 'Lab'
coinsert 'Dog'
coclass 'Collie'
coinsert 'Dog'

coclass specifies that following definitions will be within the named class, and coinsert specifies that the current class will inherit from the named classes (or object -- in J the only difference between a class and an object is its name and how you can create them -- this motivates the "co" prefix on operations which manipulate classes and objects).

See http://www.jsoftware.com/help/jforc/modular_code.htm

That said, some operations in J -- including coinsert -- will create classes if they did not already exist. So the above may be simplified to: 

coinsert_Dog_ 'Animal'
coinsert_Cat_ 'Animal'
coinsert_Lab_ 'Dog'
coinsert_Collie_ 'Dog'

That said, note that classes and objects are not "types" in J. Instead, they are components of names. In general, when we deal with objects and classes we deal with references to the underlying representation, and in J the references are names, so a collection of classes and objects, in J, would be a collection of names which refer to classes and objects. In other words, the "type" (to the degree that there is a type) would be best thought of as "name" (or, more mechanically: boxed list of characters).

[edit] Java

public class Animal{
   //functions go here...
}
public class Dog extends Animal{
   //functions go here...
}
public class Cat extends Animal{
   //functions go here...
}
public class Lab extends Dog{
   //functions go here...
}
public class Collie extends Dog{
   //functions go here...
}

[edit] JavaScript

JavaScript is a class-free, object-oriented language, and as such, it uses prototypal inheritance instead of classical inheritance. 

function Animal() {
    // ...
}
function Dog() {
    // ...
}
Dog.prototype = new Animal();
function Cat() {
    // ...
}
Cat.prototype = new Animal();
function Collie() {
    // ...
}
Collie.prototype = new Dog();
function Lab() {
    // ...
}
Lab.prototype = new Dog();
Animal.prototype.speak = function() {print("an animal makes a sound")};
 
var lab = new Lab();
lab.speak();  // shows "an animal makes a sound"

[edit] Kite

class Animal [
	#Method goes here
];
 
class Dog from Animal [
	#Method goes here	
];
 
class Lab from Dog [
	#Method goes here
];
 
class collie from Dog [
	#Method goes here
];
 


[edit] Lisaac

Section Header
+ name := ANIMAL;
// ...
Section Header
+ name := CAT;
Section Inherit
- parent : ANIMAL := ANIMAL;
// ...
Section Header
+ name := DOG;
Section Inherit
- parent : ANIMAL := ANIMAL;
// ...
Section Header
+ name := LAB;
Section Inherit
- parent : DOG := DOG;
// ...
Section Header
+ name := COLLIE;
Section Inherit
- parent : DOG := DOG;
// ...

[edit] Logtalk

There is no "class" keyword in Logtalk; an "object" keyword is used instead (Logtalk objects play the role of classes, meta-classes, instances, or prototypes depending on the relations with other objects). 

 
:- object(thing,
    instantiates(thing)).
:- end_object.
 
:- object(animal,
    specializes(thing)).
    ...
:- end_object.
 
:- object(dog,
    specializes(animal)).
    ...
:- end_object.
 
:- object(cat,
    specializes(animal)).
    ...
:- end_object.
 
:- object(lab,
    specializes(dog)).
    ...
:- end_object.
 
:- object(collie,
    specializes(dog)).
    ...
:- end_object.

[edit] Objective-C

@interface Animal : NSObject
{
  // ... 
}
// ...
@end
 
@interface Dog : Animal
{
  // ... 
}
// ...
@end
 
@interface Lab : Dog
{
  // ... 
}
// ...
@end
 
@interface Collie : Dog
{
  // ... 
}
// ...
@end
 
@interface Cat : Animal
{
  // ... 
}
// ...
@end

[edit] Objeck

 
class Animal
{ #~ ... ~# }
 
class Dog from Animal
{ #~ ... ~# }
 
class Lab from Dog
{ #~ ... ~# }
 
class Collie from Dog
{ #~ ... ~# }
 
class Cat from Animal
{ #~ ... ~# }
 

[edit] OCaml

class animal =
  object (self)
    (*functions go here...*)
  end
class dog =
  object (self)
    inherit animal
    (*functions go here...*)
  end
class cat =
  object (self)
    inherit animal
    (*functions go here...*)
  end
class lab =
  object (self)
    inherit dog
    (*functions go here...*)
  end
class collie =
  object (self)
    inherit dog
    (*functions go here...*)
  end

[edit] ooRexx

 
-- subclass of object by default
::class animal
 
::class cat subclass animal
 
::class dog subclass animal
 
::class lab subclass dog
 
::class collie subclass dog
 


[edit] OxygenBasic

 
class animal
  method show() as string
  return "Animal "
  end method
end Class
 
class dog
  from Animal Animal
  method show() as string
  return animal.show()+"dog "
  end method
end Class
 
class cat
  from animal animal
  method show() as string
  return animal.show()+"cat "
  end method
end Class
 
class Lab
  from dog dog
  method show() as string
  return dog.show()+"Lab "
  end method
end Class
 
class Collie
  from dog dog
  method show() as string
  return dog.show()+"Collie "
  end method
end Class
 
 
Collie c
print c.show 'result: Animal Dog Collie
 

[edit] Oz

class Animal
   %% ...
end
 
class Dog from Animal
   %% ... 
end
 
class Lab from Dog
   %% ... 
end
 
class Collie from Dog
   %% ... 
end
 
class Cat from Animal
   %% ... 
end

[edit] Pascal

See Delphi

[edit] Perl

package Animal;
#functions go here...
1;
package Dog;
use Animal;
@ISA = qw( Animal );
#functions go here...
1;
package Cat;
use Animal;
@ISA = qw( Animal );
#functions go here...
1;
package Lab;
use Dog;
@ISA = qw( Dog );
#functions go here...
1;
package Collie;
use Dog;
@ISA = qw( Dog );
#functions go here...
1;

The same using the MooseX::Declare module: 

use MooseX::Declare;
 
class Animal {
    # methods go here...
}
class Dog extends Animal {
    # methods go here...
}
class Cat extends Animal {
    # methods go here...
}
class Lab extends Dog {
    # methods go here...
}
class Collie extends Dog {
    # methods go here...
}

[edit] Perl 6

Works with: Rakudo version 2012.06
class Animal {}
class Dog is Animal {}
class Cat is Animal {}
class Lab is Dog {}
class Collie is Dog {}
 
say ~Collie.^parents;     # undefined type object
say ~Collie.new.^parents; # instantiated object
Output:
Dog() Animal()
Dog() Animal()

The .^parents notation indicates a method call to the object's metaobject rather than to the object itself.

[edit] PHP

class Animal {
   // functions go here...
}
 
class Dog extends Animal {
   // functions go here...
}
 
class Cat extends Animal {
   // functions go here...
}
 
class Lab extends Dog {
   // functions go here...
}
 
class Collie extends Dog {
   // functions go here...
}

[edit] PicoLisp

(class +Animal)
 
(class +Dog +Animal)
 
(class +Cat +Animal)
 
(class +Lab +Dog)
 
(class +Collie +Dog)
: (dep '+Animal)
+Animal
   +Cat
   +Dog
      +Collie
      +Lab

[edit] PureBasic

Although PureBasic is mostly used for procedural coding it has both the ability to interact with object oriented libraries and code and also the capacity to write it if needed.

[edit] Native version

Interface Animal
  Eat()
  Sleep()
EndInterface
 
Interface Cat Extends Animal
  ChaseMouse()
EndInterface
 
Interface Dog Extends Animal
  Bark()
  WagTail()
EndInterface
 
Interface Lab Extends Dog
  Swim()
EndInterface
 
Interface Collie Extends Dog  
  HeardSheep()
EndInterface

[edit] Simple OOP Version

Using the open-source precompiler SimpleOOP. 

Class Animal
EndClass
 
Class Dog Extends Animal
  Public Method Bark()
  EndMethod
EndClass
 
Class Cat Extends Animal
  Public Method Sleep()
  EndMethod
EndClass
 
Class Lab Extends Dog
  Public Method Swim()
  EndMethod
EndClass
 
Class Collie Extends Dog
  Public Method Fetch()
  EndMethod
EndClass
 
;- test the code
*Lassie.Collie = NewObject.Collie
*Lassie\Bark()
*Lassie\Fetch()

[edit] Python

Unrevised style classes: 

class Animal:
  pass #functions go here...
 
class Dog(Animal):
  pass #functions go here...
 
class Cat(Animal):
  pass #functions go here...
 
class Lab(Dog):
  pass #functions go here...
 
class Collie(Dog):
  pass #functions go here...

New style classes: 

import time
 
class Animal(object):
    def __init__(self, birth=None, alive=True):
        self.birth = birth if birth else time.time()
        self.alive = alive
    def age(self):
        return time.time() - self.birth
    def kill(self):
        self.alive = False
 
class Dog(Animal):
    def __init__(self, bones_collected=0, **kwargs):
        self.bone_collected = bones_collected
        super(Dog, self).__init__(**kwargs)
 
class Cat(Animal):
    max_lives = 9
    def __init__(self, lives=max_lives, **kwargs):
        self.lives = lives
        super(Cat, self).__init__(**kwargs)
    def kill(self):
        if self.lives>0:
            self.lives -= 1
            if self.lives == 0:
                super(Cat, self).kill()
        else:
            raise ValueError
        return self
 
class Labrador(Dog):
    def __init__(self, guide_dog=False, **kwargs):
        self.guide_dog=False
        super(Labrador, self).__init__(**kwargs)
 
class Collie(Dog):
    def __init__(self, sheep_dog=False, **kwargs):
        self.sheep_dog=False
        super(Collie, self).__init__(**kwargs)
 
lassie = Collie()
felix = Cat()
felix.kill().kill().kill()
mr_winkle = Dog()
buddy = Labrador()
buddy.kill()
print "Felix has",felix.lives, "lives, ","Buddy is %salive!"%("" if buddy.alive else "not ")
Output:
Felix has 6 lives,  Buddy is not alive!

[edit] R

[edit] S3

Inheritance is implemented by setting the object's class attribute with a character vector. 

aCollie <- "woof"
class(aCollie) <- c("Collie", "Dog", "Animal")

[edit] S4

Inheritance is implemented by using the 'contains' argument in setClass 

setClass("Animal", representation(), prototype())
setClass("Dog", representation(), prototype(), contains="Animal")
setClass("Cat", representation(), prototype(), contains="Animal")
setClass("Collie", representation(), prototype(), contains="Dog")
setClass("Lab", representation(), prototype(), contains="Dog")

[edit] Racket

 
#lang racket
 
(define animal% (class object% (super-new)))
(define dog%    (class animal% (super-new)))
(define cat%    (class animal% (super-new)))
(define lab%    (class dog% (super-new)))
(define collie% (class dog% (super-new)))
 
;; unit tests
(require rackunit)
 
(check-true (is-a? (new dog%) animal%))
(check-false (is-a? (new collie%) cat%))
 

[edit] REBOL

rebol [
	Title: "Inheritance"
	Author: oofoe
	Date: 2009-12-08
	URL: http://rosettacode.org/wiki/Inheritance
]
 
; REBOL provides subclassing through its prototype mechanism:
 
Animal: make object! [
	legs: 4
]
 
Dog: make Animal [
	says: "Woof!"
]
Cat: make Animal [
	says: "Meow..."
]
 
Lab: make Dog []
Collie: make Dog []
 
; Demonstrate inherited properties:
 
print ["Cat has" Cat/legs "legs."]
 
print ["Lab says:" Lab/says]

Output: 

Cat has 4 legs.
Lab says: Woof!

[edit] Ruby

inherited is a method defined on an instance of a Class object. It is invoked when a new subclass of the current class is defined (i.e. at the end statement of a class definition). 

class Animal
  #functions go here...
  def self.inherited(subclass)
    puts "new subclass of #{self}: #{subclass}"
  end
end
 
class Dog < Animal
  #functions go here...
end
 
class Cat < Animal
  #functions go here...
end
 
class Lab < Dog
  #functions go here...
end
 
class Collie < Dog
  #functions go here...
end

Output 

new subclass of Animal: Dog
new subclass of Dog: Lab
new subclass of Dog: Collie
new subclass of Animal: Cat

[edit] Scala

Scala has both classes and traits. Classes can only be singly inherited, but both can inherit a trait multiple times. This inheritance can be declared at the point of instantiation as well, precluding the need to declare a trait or class for the sole purpose of combining traits. For the simple inheritance chain of this task, any (or all) of the class keywords below can be replaced with trait 

class Animal
class Dog extends Animal
class Cat extends Animal
class Lab extends Dog
class Collie extends Dog

[edit] Seed7

Seed7 object orientation is based on interface types and implementation types. The example below defines a hierarchy of implementation types. 

$ include "seed7_05.s7i";
 
const type: Animal is new struct
    # ... 
  end struct;
 
const type: Dog is sub Animal struct
    # ... 
  end struct;
 
const type: Lab is sub Dog struct
    # ...
  end struct;
 
const type: Collie is sub Dog struct
    # ...
  end struct;
 
const type: Cat is sub Animal struct
    # ...
  end struct;

[edit] Slate

define: #Animal &parents: {Cloneable}.
define: #Dog &parents: {Animal}.
define: #Cat &parents: {Animal}.
define: #Lab &parents: {Dog}.
define: #Collie &parents: {Dog}.

[edit] Smalltalk

This is an example of the object serialization format used by many varieties of Smalltalk. Normally the class tree would be defined and navigated via a class browser within a graphical Smalltalk environment. 

Object subclass: #Animal
  instanceVariableNames: ' ' "* space separated list of names *"
  classVariableNames: ' '
  poolDictionaries: ' '
  category: ' ' !
 
"* declare methods here, separated with '!' *"
"* !Animal methodsFor: 'a category'! *"
"* methodName *"
"*    method body! !
 
!Animal subclass: #Dog
   "* etc. *" !
 
!Animal subclass: #Cat
  "* etc. *" !
 
!Dog subclass: #Lab
  "* etc. *" !
 
!Dog subclass: #Collie
  "* etc. *" !

[edit] Tcl

Works with: Tcl version 8.6
or
Library: TclOO
package require TclOO
oo::class create Animal {
   # ...
}
oo::class create Dog {
   superclass Animal
   # ...
}
oo::class create Cat {
   superclass Animal
   # ...
}
oo::class create Collie {
   superclass Dog
   # ...
}
oo::class create Lab {
   superclass Dog
   # ...
}

[edit] TXR

For exception symbols only. 

@(defex cat animal)
@(defex lab dog animal)
@(defex collie dog)

The second line is a shorthand which defines a lab to be a kind of dog, and at the same time a dog to be a kind of animal.

If we throw an exception of type lab, it can be caught in a catch for a dog or for an animal. Continuing with the query: 

@(try)
@  (throw lab "x")
@(catch animal (arg))
@(end)

Test: 

$ txr dog-cat.txr
arg="x"

[edit] Vorpal

pet = new()
cat = new(pet)
dog = new(pet)
fido = new(dog)
felix = new(cat)

[edit] Visual Basic .NET

Class Animal
  ' ...
End Class
 
Class Dog
  Inherits Animal
  ' ...
End Class
 
Class Lab
  Inherits Dog
  ' ...
End Class
 
Class Collie
  Inherits Dog
  ' ...
End Class
 
Class Cat
  Inherits Animal
  ' ...
End Class
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