Inheritance/Single

Inheritance/Single
You are encouraged to solve this task according to the task description, using any language you may know.

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```

ActionScript

<lang actionscript>public class Animal {

```   // ...
```

}</lang> <lang actionscript>public class Cat extends Animal {

```   // ...
```

}</lang> <lang actionscript>public class Dog extends Animal {

```   // ...
```

}</lang> <lang actionscript>public class Lab extends Dog {

```   // ...
```

}</lang> <lang actionscript>public class Collie extends Dog {

```   // ...
```

}</lang>

```  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;</lang>

Aikido

<lang aikido >class Animal{

```  //functions go here...
```

}</lang> <lang aikido >class Dog extends Animal {

```  //functions go here...
```

}</lang> <lang aikido >class Cat extends Animal {

```  //functions go here...
```

}</lang> <lang aikido >class Lab extends Dog {

```  //functions go here...
```

}</lang> <lang aikido >class Collie extends Dog {

```  //functions go here...
```

}</lang>

AutoHotkey

Works with: AutoHotkey_L

AutoHotkey_L is prototype-based. However, for convenience, class-syntax may be used to create a base object. <lang AutoHotkey>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 { }</lang>

BBC BASIC

<lang bbcbasic> 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 Collie{method}
PROC_inherit(Collie{}, Dog{})
PROC_class(Collie{})</lang>
```

C++

<lang cpp>class Animal {

``` // ...
```

};

class Dog: public Animal {

``` // ...
```

};

class Lab: public Dog {

``` // ...
```

};

class Collie: public Dog {

``` // ...
```

};

class Cat: public Animal {

``` // ...
```

};</lang>

C#

<lang csharp>class Animal {

``` /* ... */
// ...
```

}

class Dog : Animal {

``` /* ... */
// ...
```

}

class Lab : Dog {

``` /* ... */
// ...
```

}

class Collie : Dog {

``` /* ... */
// ...
```

}

class Cat : Animal {

``` /* ... */
// ...
```

}</lang>

Clojure

This is not very useful in clojure

<lang 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)</lang>

More useful:

<lang Clojure>(derive ::dog ::animal) (derive ::cat ::animal) (derive ::lab ::dog) (derive ::collie ::dog)</lang>

use:

<lang Clojure>user> (isa? ::dog ::animal) true user> (isa? ::dog ::cat) false user> (isa? ::collie ::animal) true</lang>

COBOL

<lang cobol> CLASS-ID. Animal.

```          *> ...
END CLASS Animal.

CLASS-ID. Dog INHERITS Animal.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
CLASS Animal.
```
```          *> ...
END CLASS Dog.

CLASS-ID. Cat INHERITS Animal.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
CLASS Animal.
```
```          *> ...
END CLASS Cat.

CLASS-ID. Lab INHERITS Dog.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
CLASS Dog.
```
```          *> ...
END CLASS Lab.

CLASS-ID. Collie INHERITS Dog.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
CLASS Dog.
```
```          *> ...
END CLASS Collie.</lang>
```

Common Lisp

Using CLOS classes, we have the following:

<lang lisp>(defclass animal () ()) (defclass dog (animal) ()) (defclass lab (dog) ()) (defclass collie (dog) ()) (defclass cat (animal) ())</lang>

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

<lang lisp>(defstruct animal) (defstruct (dog (:include animal))) (defstruct (lab (:include dog))) (defstruct (collie (:include dog))) (defstruct (cat (:include animal)))</lang>

(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.

<lang lisp>

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))

``` #| ... #|
)</lang>
```

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.

Component Pascal

<lang oberon2> 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; </lang>

D

<lang d>class Animal {

```   // ...
```

}

class Dog: Animal {

```   // ...
```

}

class Lab: Dog {

```   // ...
```

}

class Collie: Dog {

```   // ...
```

}

class Cat: Animal {

```   // ...
```

}

void main() {}</lang>

Delphi

<lang 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);</lang>
```

DWScript

<lang Delphi>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;</lang>

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.

<lang e>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]
```

}</lang>

Setting up the task's specified tree:

<lang e>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])</lang>

Some example objects:

<lang e>def fido implements LabStamp {} def tom implements CatStamp {} def brick {} # not an animal</lang>

Testing against the types:

<lang e>? fido :Animal

1. value: <fido>

? fido :Cat

1. problem: <fido> is not a Cat

? fido :Lab

1. value: <fido>

? tom :Animal

1. value: <tom>

? tom :Cat

1. value: <tom>

? brick :Animal

1. problem: <brick> is not a Animal</lang>

Eiffel

<lang eiffel >class

```   ANIMAL
```

end</lang> <lang eiffel >class

```   DOG
```

inherit

```   ANIMAL
```

end</lang> <lang eiffel >class

```   CAT
```

inherit

```   ANIMAL
```

end</lang> <lang eiffel >class

```   LAB
```

inherit

```   DOG
```

end</lang> <lang eiffel >class

```   COLLIE
```

inherit

```   DOG
```

end</lang>

Factor

<lang factor>TUPLE: animal ; TUPLE: dog < animal ; TUPLE: cat < animal ; TUPLE: lab < dog ; TUPLE: collie < dog ;</lang>

Fancy

<lang fancy>class Animal {

``` # ...
```

}

class Dog : Animal {

``` # ...
```

}

class Cat : Animal {

``` # ...
```

}

class Lab : Dog {

``` # ...
```

}

class Collie : Dog {

``` # ...
```

}</lang>

Fantom

<lang fantom>class Animal { }

class Dog : Animal { }

class Cat : Animal { }

class Lab : Dog { }

class Collie : Dog { }</lang>

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. <lang forth>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 {} ;</lang>

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).

<lang fortran>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</lang>

F#

The `()` behind the class names indicates a public default constructor; you need some type of public constructor to derive from a class. <lang fsharp>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()</lang>
```

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. <lang go>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"
```

} </lang>

Groovy

<lang groovy>class Animal{

```  //contents go here...
```

}</lang> <lang groovy>class Dog extends Animal{

```  //contents go here...
```

}</lang> <lang groovy>class Cat extends Animal{

```  //contents go here...
```

}</lang> <lang groovy>class Lab extends Dog{

```  //contents go here...
```

}</lang> <lang groovy>class Collie extends Dog{

```  //contents go here...
```

}</lang>

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.

<lang haskell>class Animal a class Animal a => Cat a class Animal a => Dog a class Dog a => Lab a class Dog a => Collie a</lang>

Haxe

<lang haxe>class Animal {

```   // ...
```

}</lang> <lang haxe>class Cat extends Animal {

```   // ...
```

}</lang> <lang haxe>class Dog extends Animal {

```   // ...
```

}</lang> <lang haxe>class Lab extends Dog {

```   // ...
```

}</lang> <lang haxe>class Collie extends Dog {

```   // ...
```

}</lang>

Icon and Unicon

This example only works in Unicon.

<lang Unicon> class Animal () end

class Dog : Animal () end

class Cat : Animal () end

class Lab : Dog () end

class Collie : Dog () end </lang>

Inform 7

<lang inform7>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.</lang>

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

Io

<lang io>Animal := Object clone Cat := Animal clone Dog := Animal clone Collie := Dog clone Lab := Dog clone</lang>

J

Here is how this would normally be done:

<lang j>coclass 'Animal'</lang> <lang j>coclass 'Dog' coinsert 'Animal'</lang> <lang j>coclass 'Cat' coinsert 'Animal'</lang> <lang j>coclass 'Lab' coinsert 'Dog'</lang> <lang j>coclass 'Collie' coinsert 'Dog'</lang>

`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).

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

<lang j>coinsert_Dog_ 'Animal' coinsert_Cat_ 'Animal' coinsert_Lab_ 'Dog' coinsert_Collie_ 'Dog'</lang>

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).

Java

<lang java>public class Animal{

```  //functions go here...
```

}</lang> <lang java>public class Dog extends Animal{

```  //functions go here...
```

}</lang> <lang java>public class Cat extends Animal{

```  //functions go here...
```

}</lang> <lang java>public class Lab extends Dog{

```  //functions go here...
```

}</lang> <lang java>public class Collie extends Dog{

```  //functions go here...
```

}</lang>

JavaScript

JavaScript is a class-free, object-oriented language, and as such, it uses prototypal inheritance instead of classical inheritance. <lang javascript>function Animal() {

```   // ...
```

}</lang>

<lang javascript>function Dog() {

```   // ...
```

} Dog.prototype = new Animal();</lang>

<lang javascript>function Cat() {

```   // ...
```

} Cat.prototype = new Animal();</lang>

<lang javascript>function Collie() {

```   // ...
```

} Collie.prototype = new Dog();</lang>

<lang javascript>function Lab() {

```   // ...
```

} Lab.prototype = new Dog();</lang>

<lang javascript>Animal.prototype.speak = function() {print("an animal makes a sound")};

var lab = new Lab(); lab.speak(); // shows "an animal makes a sound"</lang>

Kite

<lang 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 ]; </lang>

Lasso

<lang Lasso>define animal => type { data public gender::string }

define dog => type { parent animal }

define cat => type { parent animal }

define collie => type { parent dog }

define lab => type { parent dog }

local(myanimal = lab)

1. myanimal -> gender = 'Male'
2. myanimal -> gender</lang>

-> Male

Lisaac

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

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). <lang logtalk>

- 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.</lang>

Nemerle

<lang nemerle>class Animal {

```   // ...
```

}

class Dog: Animal {

```   // ...
```

}

class Lab: Dog {

```   // ...
```

}

class Collie: Dog {

```   // ...
```

}

class Cat: Animal {

```   // ...
```

}</lang>

NetRexx

Class names cosmetically augmented slightly to prevent namespace pollution.

For brevity, all classes are defined within the same source file. Normally classes exist as separate source units. <lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols binary

class RInheritSingle public

``` method main(args = String[]) public static
animals = [ -
RInheritSingle_Animal(), -
RInheritSingle_Cat(), -
RInheritSingle_Dog(), -
RInheritSingle_Lab(), -
RInheritSingle_Collie() -
]
```
```   say 'Object ID'.left(12) 'Class type'.left(24)  'Superclass type'
say '.'.left(12, '.')    '.'.left(24, '.')      '.'.left(24, '.')
loop animal over animals
parse animal.whatAmI() oid ct st
say oid.left(12) ct.left(24) st
end animal
return
```

class RInheritSingle_Animal private

``` properties indirect
whatThatIs = String
whatThisIs = String
method RInheritSingle_Animal() public
-- Animal specific set-up
setWhatThatIs(this.getClass().getSuperclass().getSimpleName())
setWhatThisIs(this.getClass().getSimpleName())
return
method hashToString() public
return '@'(Rexx this.hashCode()).d2x().right(8, 0)
method whatAmI() public
iAmText = hashToString() getWhatThisIs() getWhatThatIs()
return iAmText
```

class RInheritSingle_Cat private extends RInheritSingle_Animal

``` method RInheritSingle_Cat() public
-- Do Cat specific set-up
return
```

class RInheritSingle_Dog private extends RInheritSingle_Animal

``` method RInheritSingle_Dog() public
-- Do Dog specific set-up
return
```

class RInheritSingle_Lab private extends RInheritSingle_Dog

``` method RInheritSingle_Lab() public
-- Do Lab specific set-up
return
```

class RInheritSingle_Collie private extends RInheritSingle_Dog

``` method RInheritSingle_Collie() public
-- Do Collie specific set-up
return
```

</lang>

Output:
```Object ID    Class type               Superclass type
............ ........................ ........................
@3F81D405    RInheritSingle_Animal    Object
@51430296    RInheritSingle_Cat       RInheritSingle_Animal
@065EEF88    RInheritSingle_Dog       RInheritSingle_Animal
@42BFCCFC    RInheritSingle_Lab       RInheritSingle_Dog
```

Objective-C

<lang objc>@interface Animal : NSObject {

``` // ...
```

} // ... @end

@interface Dog : Animal {

``` // ...
```

} // ... @end

@interface Lab : Dog {

``` // ...
```

} // ... @end

@interface Collie : Dog {

``` // ...
```

} // ... @end

@interface Cat : Animal {

``` // ...
```

} // ... @end</lang>

Objeck

<lang objeck> class Animal { #~ ... ~# }

class Dog from Animal { #~ ... ~# }

class Lab from Dog { #~ ... ~# }

class Collie from Dog { #~ ... ~# }

class Cat from Animal { #~ ... ~# } </lang>

OCaml

<lang ocaml>class animal =

``` object (self)
(*functions go here...*)
end</lang>
```

<lang ocaml>class dog =

``` object (self)
inherit animal
(*functions go here...*)
end</lang>
```

<lang ocaml>class cat =

``` object (self)
inherit animal
(*functions go here...*)
end</lang>
```

<lang ocaml>class lab =

``` object (self)
inherit dog
(*functions go here...*)
end</lang>
```

<lang ocaml>class collie =

``` object (self)
inherit dog
(*functions go here...*)
end</lang>
```

ooRexx

<lang ooRexx> -- subclass of object by default

class animal
class cat subclass animal
class dog subclass animal
class lab subclass dog
class collie subclass dog

</lang>

OxygenBasic

<lang 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 </lang>

Oz

<lang oz>class Animal

```  %% ...
```

end

class Dog from Animal

```  %% ...
```

end

class Lab from Dog

```  %% ...
```

end

class Collie from Dog

```  %% ...
```

end

class Cat from Animal

```  %% ...
```

end</lang>

See Delphi

Perl

<lang perl>package Animal;

1. functions go here...

1;</lang>

<lang perl>package Dog; use Animal; @ISA = qw( Animal );

1. functions go here...

1;</lang>

<lang perl>package Cat; use Animal; @ISA = qw( Animal );

1. functions go here...

1;</lang>

<lang perl>package Lab; use Dog; @ISA = qw( Dog );

1. functions go here...

1;</lang>

<lang perl>package Collie; use Dog; @ISA = qw( Dog );

1. functions go here...

1;</lang>

The same using the MooseX::Declare module:

<lang perl>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...
```

}</lang>

Perl 6

Works with: Rakudo version 2012.06

<lang perl6>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</lang>

Output:
```Dog() Animal()
Dog() Animal()```

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

PHP

<lang 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...
```

}</lang>

PicoLisp

<lang PicoLisp>(class +Animal)

(class +Dog +Animal)

(class +Cat +Animal)

(class +Lab +Dog)

(class +Collie +Dog)</lang> <lang PicoLisp>: (dep '+Animal) +Animal

```  +Cat
+Dog
+Collie
+Lab</lang>
```

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.

Native version

<lang PureBasic>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</lang>

Simple OOP Version

Using the open-source precompiler SimpleOOP. <lang PureBasic>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()</lang>

Python

Unrevised style classes: <lang python>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...</lang>
```

New style classes: <lang python>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
```

```   def __init__(self, guide_dog=False, **kwargs):
self.guide_dog=False
```

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 ")</lang>

Output:
```Felix has 6 lives,  Buddy is not alive!
```

R

S3

Inheritance is implemented by setting the object's class attribute with a character vector. <lang R>aCollie <- "woof" class(aCollie) <- c("Collie", "Dog", "Animal")</lang>

S4

Inheritance is implemented by using the 'contains' argument in setClass <lang R>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")</lang>

Racket

<lang racket>

1. 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%)) </lang>

REBOL

<lang 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]</lang>

Output:

```Cat has 4 legs.
Lab says: Woof!```

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). <lang ruby>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</lang>

Output

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

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`

<lang scala>class Animal class Dog extends Animal class Cat extends Animal class Lab extends Dog class Collie extends Dog</lang>

Seed7

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

<lang seed7>\$ 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;</lang>
```

Slate

<lang slate>define: #Animal &parents: {Cloneable}. define: #Dog &parents: {Animal}. define: #Cat &parents: {Animal}. define: #Lab &parents: {Dog}. define: #Collie &parents: {Dog}.</lang>

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. <lang smalltalk>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. *" !</lang>
```

Tcl

Works with: Tcl version 8.6
or
Library: TclOO

<lang tcl>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
# ...
```

}</lang>

TXR

For exception symbols only.

<lang txr>@(defex cat animal) @(defex lab dog animal) @(defex collie dog)</lang>

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:

<lang txr>@(try) @ (throw lab "x") @(catch animal (arg)) @(end)</lang>

Test:

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

Vorpal

<lang vorpal>pet = new() cat = new(pet) dog = new(pet) fido = new(dog) felix = new(cat)</lang>

Visual Basic .NET

<lang vbnet>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</lang>