Inheritance/Multiple

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

Multiple inheritance allows to specify that one class is a subclass of several other classes.

Some languages allow multiple inheritance for arbitrary classes,   others restrict it to interfaces,   some don't allow it at all.

Task

Write two classes (or interfaces) Camera and MobilePhone,   then write a class CameraPhone which is both a Camera and a MobilePhone.

There is no need to implement any functions for those classes.

Ada

Ada 2005 has added interfaces, allowing a limited form of multiple inheritance.

package Multiple_Interfaces is
   type Camera is tagged null record;
   type Mobile_Phone is limited Interface;
   type Camera_Phone is new Camera and Mobile_Phone with null record;
end Multiple_Interfaces;

Aikido

Aikido does not support multiple inheritance, but does allow multiple implementation of interfaces.

interface Camera {
}

interface Mobile_Phone {
}

class Camera_Phone implements Camera, Mobile_Phone {
}

BBC BASIC

Works with: BBC BASIC for Windows

      INSTALL @lib$+"CLASSLIB"
      
      DIM Camera{TakePicture}
      PROC_class(Camera{})
      
      DIM MobilePhone{MakeCall}
      PROC_class(MobilePhone{})
      
      DIM CameraPhone{methods}
      PROC_inherit(CameraPhone{}, Camera{})
      PROC_inherit(CameraPhone{}, MobilePhone{})
      PROC_class(CameraPhone{})

C

C simulates Multiple Inheritance via Structures.

typedef struct{
	double focalLength;
	double resolution;
	double memory;
}Camera;

typedef struct{
	double balance;
	double batteryLevel;
	char** contacts;
}Phone;

typedef struct{
	Camera cameraSample;
	Phone phoneSample;
}CameraPhone;

C#

In C# you may inherit from only one class, but you can inherit from multiple interfaces. Also, in C# it is standard practice to start all interface names with a capital 'I' so I have altered the name of the interface. In the example we inherit from a class and an interface.

interface ICamera {
    // ...
}

class MobilePhone {
    // ...
}

class CameraPhone: ICamera, MobilePhone {
    // ...
}

C++

class Camera
{
  // ...
};

class MobilePhone
{
  // ...
};

class CameraPhone:
  public Camera,
  public MobilePhone
{
  // ...
};

Clojure

(defprotocol Camera)

(defprotocol MobilePhone)

(deftype CameraPhone []
  Camera
  MobilePhone)

COBOL

       IDENTIFICATION DIVISION.
       CLASS-ID. Camera.
           *> ...
       END CLASS Camera.
       
       IDENTIFICATION DIVISION.
       CLASS-ID. Mobile-Phone.
           *> ...
       END CLASS Mobile-Phone.
       
       IDENTIFICATION DIVISION.
       CLASS-ID. Camera-Phone
           INHERITS FROM Camera, Mobile-Phone.    
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       REPOSITORY.
           CLASS Camera
           CLASS Mobile-Phone.
           
           *> ...
       END CLASS Camera-Phone.

Common Lisp

(defclass camera () ())
(defclass mobile-phone () ())
(defclass camera-phone (camera mobile-phone) ())

D

While D does not have multiple base class inheritance, you can inherit from multiple interfaces.

interface Camera {
    // member function prototypes and static methods
}

interface MobilePhone {
    // member function prototypes and static methods
}

class CameraPhone: Camera, MobilePhone {
    // member function implementations for Camera,
    //   MobilePhone, and CameraPhone
}

D also supports the non-virtual interface pattern, where an interface may have non-virtual methods with defined implementations.

interface Camera {
    // A virtual function.
    Image takePhoto();

    // A non-virtual function.
    final Image[] takeSeveralPhotos(int count) {
        auto result = new Image[count];
        foreach (ref img; result) {
            img = takePhoto();
        }
    }
}

In addition, D's alias this feature allows one to create a type that, while it does not technically derive from two different classes, behaves as if it did.

class A {
    string foo() {
        return "I am an A.";
    }
}
class B {
    string foo() {
        return "I am a B.";
    }
}

class C : A {
    string className = "C";
    override string foo() {
        return "I am a "~className~", and thus an A.";
    }
    @property
    BWrapper asB() {
        return new BWrapper();
    }
    alias asB this;
    class BWrapper : B {
        override string foo() {
            return "I am a "~className~", disguised as a B.";
        }
    }
}

unittest {
    import std.stdio : writeln;
    
    auto c = new C();
    A a = c;
    B b = c;
    
    writeln(a.foo());
    writeln(b.foo());
}

You can currently only have a single alias this, but multiple alias this is planned. Nested alias this works today, but is somewhat finicky.

Lastly, D has template and string mixins. These can be used for static polymorphism, where a piece of code is written once and has a single definition, but is used in multiple places. It does not enable any sort of dynamic polymorphism that is not covered above.

template registerable() {
    void register() { /* implementation */ }
}

string makeFunction(string s) {
    return `string `~s~`(){ return "`~s~`";}`;
}

class Foo {
    mixin registerable!();
    mixin(makeFunction("myFunction"));
}

unittest {
    import std.stdio : writeln;
    Foo foo = new Foo;
    foo.register();
    writeln(foo.myFunction());
}

Using D's CTFE and reflection capabilities, string mixins can copy the interface of other types, and thus be used for proxies and mocks.

Delphi

Delphi doesn't support multiple inheritance, but it does have multiple interfaces.

type
  ICamera = Interface
    // ICamera methods...
  end;

  IMobilePhone = Interface
    // IMobilePhone methods...
  end;

  TCameraPhone = class(TInterfacedObject, ICamera, IMobilePhone)
    // ICamera and IMobilePhone methods...
  end;

DWScript

See Delphi.

E

E does not have multiple inheritance as a built-in feature. In fact, E only has inheritance at all as a light syntactic sugar over delegation (message forwarding). However, using that facility it is possible to implement multiple inheritance.

This is a quick simple implementation of multiple inheritance. It simply searches (depth-first and inefficiently) the inheritance tree for a method; it does not do anything about diamond inheritance. These shortcomings could be fixed if more powerful multiple inheritance were needed.

def minherit(self, supers) {
    def forwarder match [verb, args] {
        escape __return {
            if (verb == "__respondsTo") {
                def [verb, arity] := args
                for super ? (super.__respondsTo(verb, arity)) in supers {
                    return true
                }
                return false
            } else if (verb == "__getAllegedType") {
                # XXX not a complete implementation
                return supers[0].__getAllegedType()
            } else {
                def arity := args.size()
                for super ? (super.__respondsTo(verb, arity)) in supers {
                    return E.call(super, verb, args)
                }
                throw(`No parent of $self responds to $verb/$arity`)
            }
        }
    }
    return forwarder
}

The task example:

def makeCamera(self) {
    return def camera extends minherit(self, []) {
        to takesPictures() { return true }
    }
}

def makeMobilePhone(self) {
    return def mobilePhone extends minherit(self, []) {
        to makesCalls() { return true }
        to internalMemory() { return 64*1024 }
    }
}

def makeCameraPhone(self) {
    return def cameraPhone extends minherit(self, [
        makeCamera(self),
        makeMobilePhone(self),
    ]) {
        to internalMemory() {
            return super.internalMemory() + 32 * 1024**2
        }
    }
}

And testing that it works as intended:

? def p := makeCameraPhone(p)
> [p.takesPictures(), p.makesCalls(), p.internalMemory()]
# value: [true, true, 33619968]

Eiffel

Having two class—one for CAMERA and the other for a MOBILE_PHONE ...

class
    CAMERA
end

class
    MOBILE_PHONE
end

Now Multiple Inherit

We can create a new CAMERA_PHONE, which inherits directly from both CAMERA and MOBILE_PHONE.

class
    CAMERA_PHONE
inherit
    CAMERA
    MOBILE_PHONE
end

NOTE: There is no reasonable limit to the number of classes we can inherit from in a single class. The compiler helps us to navigate issues like repeated inheritance and the "diamond of death" easily and quickly.

Elena

ELENA only permits inheritance from one parent class. However, mixins are supported

singleton CameraFeature
{
    cameraMsg
        = "camera";
}
 
class MobilePhone
{
    mobileMsg
        = "phone";
}
 
class CameraPhone : MobilePhone
{
    dispatch() => CameraFeature;
}
 
public program()
{
   var cp := new CameraPhone();
 
   console.writeLine(cp.cameraMsg);
   console.writeLine(cp.mobileMsg)
}

Alternatively a group object may be created

import system'dynamic;

class CameraFeature
{
    cameraMsg
        = "camera";
}

class MobilePhone
{
    mobileMsg
        = "phone";
}

singleton CameraPhone
{
   new() = new MobilePhone().mixInto(new CameraFeature());
}

public program()
{
   var cp := CameraPhone.new();

   console.writeLine(cp.cameraMsg);
   console.writeLine(cp.mobileMsg)
}

F#

A class can only inherit from one other class, but it can implement any number of interfaces.

type Picture = System.Drawing.Bitmap // (a type synonym)

// an interface type
type Camera =
  abstract takePicture : unit -> Picture

// an interface that inherits multiple interfaces
type Camera2 =
  inherits System.ComponentModel.INotifyPropertyChanged 
  inherits Camera

// a class with an abstract method with a default implementation
// (usually called a virtual method)
type MobilePhone() =
  abstract makeCall : int[] -> unit
  default x.makeCall(number) = () // empty impl

// a class that inherits from another class and implements an interface
type CameraPhone() =
  inherit MobilePhone()
  interface Camera with
    member x.takePicture() = new Picture(10, 10)

Factor

TUPLE: camera ;
TUPLE: mobile-phone ;
UNION: camera-phone camera mobile-phone ;

Fantom

Fantom only permits inheritance from one parent class. However, Fantom supports 'mixins': a mixin is a collection of implemented methods to be added to the child class. Any number of mixins can be added to any given child class. It is an error for method names to conflict.

// a regular class
class Camera
{
  Str cameraMsg ()
  {
    "camera"
  }
}

// a mixin can only contain methods
mixin MobilePhone
{
  Str mobileMsg ()
  {
    "mobile phone"
  }
}

// class inherits from Camera, and mixes in the methods from MobilePhone
class CameraPhone : Camera, MobilePhone
{
}

class Main
{
  public static Void main ()
  {
    cp := CameraPhone ()
    echo (cp.cameraMsg)
    echo (cp.mobileMsg)
  }
}

Forth

Standard Forth does not supply high level data structures or functions. But there is library code written by vendors or users. For object programming with multiple inheritance there is a user-supplied ANS compatible extension.

https://github.com/DouglasBHoffman/FMS2 Download the FMSMI package to run the following example code.

 

\ define class camera with method say:
:class camera
 :m say: ." camera " ;m
;class

\ define class phone with method say:
:class phone
 :m say: ." phone " ;m
;class

\ define cameraPhone phone with method say:
\ class cameraPhone inherits from both class
\ camera and class phone
:class cameraPhone super{ camera phone }
 :m say: self say: \ method conflicts in superclasses
                   \ are resolved by left-to-right order
                   \ so self say: will call the say: method
                   \ from class camera
    super> phone say: \ super> phone is used to direct
                      \ this say: method to use the
                      \ method from class phone
 ;m
;class

cameraPhone cp \ instantiate a cameraPhone object named cp

cp say: \ send the say: message to cp

\ output:
camera phone

FreeBASIC

' FB 1.05.0 Win64

' FB does not currently support multiple inheritance. Composition has to be used instead if one wants
' to (effectively) inherit from more than one class. In some cases, this might arguably be a better 
' solution anyway.

Type Camera Extends Object  ' if virtual methods etc needed
  ' ...  
End Type

Type Phone Extends Object
  ' ...
End Type

Type CameraPhone Extends Phone ' single inheritance
  cam As Camera ' using composition here
  ' other stuff
End Type

Go

Go abandons traditional object oriented concepts of inheritance hierarchies, yet it does have features for composing both structs and interfaces.

// Example of composition of anonymous structs
package main

import "fmt"

// Two ordinary structs
type camera struct {
    optics, sensor string
}

type mobilePhone struct {
    sim, firmware string
}

// Fields are anonymous because only the type is listed.
// Also called an embedded field.
type cameraPhone struct {
    camera
    mobilePhone
}

func main() {
    // Struct literals must still reflect the nested structure
    htc := cameraPhone{camera{optics: "zoom"}, mobilePhone{firmware: "3.14"}}

    // But fields of anonymous structs can be referenced without qualification.
    // This provides some effect of the two parent structs being merged, as
    // with multiple inheritance in some other programming languages.
    htc.sim = "XYZ"
    fmt.Println(htc)
}

Output:

(Note sensor field still blank)

{{zoom } {XYZ 3.14}}

// Example of composition of interfaces.
// Types implement interfaces simply by implementing functions.
// The type does not explicitly declare the interfaces it implements.
package main

import "fmt"

// Two interfaces.
type camera interface {
    photo()
}

type mobilePhone interface {
    call()
}

// Compose interfaces.  cameraPhone interface now contains whatever
// methods are in camera and mobilePhone.
type cameraPhone interface {
    camera
    mobilePhone
}

// User defined type.
type htc int

// Once the htc type has this method defined on it, it automatically satisfies
// the camera interface.
func (htc) photo() {
    fmt.Println("snap")
}

// And then with this additional method defined, it now satisfies both the
// mobilePhone and cameraPhone interfaces.
func (htc) call() {
    fmt.Println("omg!")
}

func main() {
    // type of i is the composed interface.  The assignment only compiles
    // because static type htc satisfies the interface cameraPhone.
    var i cameraPhone = new(htc)
    // interface functions can be called without reference to the
    // underlying type.
    i.photo()
    i.call()
}

Output:

snap
omg!

Groovy

Same inheritance rules as Java.

Haskell

class Camera a
class MobilePhone a
class (Camera a, MobilePhone a) => CameraPhone a

Icon and Unicon

Icon does not support classes or inheritance. An intermediate language called Idol was developed as proof of concept for extending Icon. This became one of the major addons contributing to Unicon.

class Camera (instanceVars)
    # methods...
    # initializer...
end

class Phone (instanceVars)
    # methods...
    # initializer...
end

class CameraPhone : Camera, Phone (instanceVars)
    # methods...
    # initialiser...
end

Io

Camera := Object clone
Camera click := method("Taking snapshot" println)

MobilePhone := Object clone
MobilePhone call := method("Calling home" println)

CameraPhone := Camera clone
CameraPhone appendProto(MobilePhone)

myPhone := CameraPhone clone
myPhone click	// --> "Taking snapshot"
myPhone call	// --> "Calling home"

In Io each object has an internal list of prototype objects it inherits from. You can add to this list with appendProto.

Ioke

Camera = Origin mimic
MobilePhone = Origin mimic
CameraPhone = Camera mimic mimic!(MobilePhone)

J

coclass 'Camera'

create=: verb define
  NB. creation-specifics for a camera go here
)

destroy=: codestroy

NB. additional camera methods go here

coclass 'MobilePhone'

create=: verb define
  NB. creation-specifics for a mobile phone go here
)

destroy=: codestroy

NB. additional phone methods go here

coclass 'CameraPhone'
coinsert 'Camera MobilePhone'

create=: verb define
  create_Camera_ f. y
  create_MobilePhone_ f. y
  NB. creation details specific to a camera phone go here
)

destroy=: codestroy 

NB. additional camera-phone methods go here

The adverb Fix (f.) is needed as shown so the superclass constructors get executed in the object, not in the superclass.

Java

Java does not allow multiple inheritance, but you can "implement" multiple interfaces. All methods in interfaces are abstract (they don't have an implementation). When you implement an interface you need to implement the specified methods.

public interface Camera{
   //functions here with no definition...
   //ex:
   //public void takePicture();
}

public interface MobilePhone{
   //functions here with no definition...
   //ex:
   //public void makeCall();
}

public class CameraPhone implements Camera, MobilePhone{
   //functions here...
}

Julia

Julia supports inheritance via abstract types. In Julia, multiple dispatch allows objects of different types to have the same function interfaces. Julia also can support traits via parameters in type declarations or with macros. This makes multiple inheritance in Julia mostly unnecessary, except for the inconvenience of composing the data in a mixed type when declaring multiple similar types, for which there are macros.

For example, the functions dialnumber(equipment, name) and video(equipment, filename) could be used as generic interfaces to implement methods for a Telephone, a Camera, and a SmartPhone, and Julia would dispatch according to the type of the equipment.

abstract type Phone end

struct DeskPhone <: Phone
    book::Dict{String,String}
end

abstract type Camera end

struct kodak
    roll::Vector{Array{Int32,2}}
end

struct CellPhone <: Phone
    book::Dict{String,String}    
    roll::Vector{AbstractVector}    
end

function dialnumber(phone::CellPhone)
    println("beep beep")
end

function dialnumber(phone::Phone)
    println("tat tat tat tat")
end

function snap(camera, img)
    println("click")
    push!(camera.roll, img)
end

dphone = DeskPhone(Dict(["information" => "411"]))
cphone = CellPhone(Dict(["emergency" => "911"]), [[]])

dialnumber(dphone)
dialnumber(cphone)

Output:

tat tat tat tat
beep beep

Kotlin

Interfaces in Kotlin are very similar to Java 8. They can contain declarations of abstract methods, as well as method implementations.
What makes them different from abstract classes is that interfaces cannot store state. They can have properties but these need to be abstract or to provide accessor implementations.

interface Camera {
    val numberOfLenses : Int
}

interface MobilePhone {
    fun charge(n : Int) {
        if (n >= 0) 
            battery_level = (battery_level + n).coerceAtMost(100)
    }

    var battery_level : Int
}

data class CameraPhone(override val numberOfLenses : Int = 1, override var battery_level: Int) : Camera, MobilePhone
data class TwinLensCamera(override val numberOfLenses : Int = 2) : Camera

fun main(args: Array<String>) {
    val c = CameraPhone(1, 50)
    println(c)
    c.charge(35)
    println(c)
    c.charge(78)
    println(c)
    println(listOf(c.javaClass.superclass) + c.javaClass.interfaces)
    val c2 = TwinLensCamera()
    println(c2)
    println(listOf(c2.javaClass.superclass) + c2.javaClass.interfaces)
}

Output:

CameraPhone(numberOfLenses=1, battery_level=50)
CameraPhone(numberOfLenses=1, battery_level=85)
CameraPhone(numberOfLenses=1, battery_level=100)
[class java.lang.Object, interface multiple_inheritance.Camera, interface multiple_inheritance.MobilePhone]
TwinLensCamera(numberOfLenses=2)
[class java.lang.Object, interface multiple_inheritance.Camera]

Lasso

Lasso only allow single inheritance. But it supports the use of multiple traits and trays hand down the methods it has implemented provided that the type fulfills the requirements for the trait. http://lassoguide.com/language/traits.html

define trait_camera => trait {
	require zoomfactor

	provide has_zoom() => {
		return .zoomfactor > 0
	}

}

define trait_mobilephone => trait {
	require brand

	provide is_smart() => {
		return .brand == 'Apple'
	}

}

define cameraphone => type {

	trait {
		import trait_camera, trait_mobilephone
	}

	data public zoomfactor::integer = 0,
		public brand::string

}

local(mydevice = cameraphone)

#mydevice -> brand = 'Apple'
#mydevice -> zoomfactor = 0

#mydevice -> has_zoom
'<br />'
#mydevice -> is_smart

-> false

true

Latitude

Latitude is a prototype-oriented language, and every object can have only one prototype. As such, multiple inheritance in the usual sense is impossible in Latitude. The behavior of multiple (implementation) inheritance can be approximated with mixins.

Camera ::= Mixin clone.
MobilePhone ::= Mixin clone.

CameraPhone ::= Object clone.
Camera inject: CameraPhone.
MobilePhone inject: CameraPhone.

In order to add functionality to either of the mixins, the interface slot of the mixin must be modified to include the name of the new method. Injecting a mixin makes a copy of the methods, as opposed to traditional (prototype) inheritance in which method calls are delegated.

Lingo

Lingo does not support multiple inheritance. But its slightly idiosyncratic inheritance implementation based on "ancestors" allows to assign/change inheritance relations at runtime. So a similar (but not identical) effect can be achieved by something like this:

-- parent script "Camera"
property resolution

on new (me)
  me.resolution = "1024x768"
  return me
end

on snap (me)
  put "SNAP!"
end

-- parent script "MobilePhone"
property ringtone

on new (me)
  me.ringtone = "Bell"
  return me
end

on ring (me, n)
  repeat with i = 1 to n
    put "RING!!!"
  end repeat
end

-- parent script "CameraPhone"
property ancestor

on new (me)
  c = script("Camera").new()
  mp = script("MobilePhone").new()

  -- make the Camera instance a parent of the MobilePhone instance
  mp.setProp(#ancestor, c)

  -- make the MobilePhone instance a parent of this CameraPhone instance
  me.ancestor = mp

  return me
end

Usage:

cp = script("CameraPhone").new()

cp.snap()
-- "SNAP!"

cp.ring(3)
-- "RING!!!"
-- "RING!!!"
-- "RING!!!"

put cp.resolution
-- "1024x768"

put cp.ringtone
-- "Bell"

Logtalk

Logtalk supports multiple inheritance. 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(camera,
    ...).
    ...
:- end_object.

:- object(mobile_phone,
    ...).
    ...
:- end_object.

:- object(camera_phone,
    specializes(camera, mobile_phone),
    ...).
    ...
:- end_object.

Lua

Lua is prototype-based. A table cannot have more than one metatable, but it can reference more than one in its __index metamethod, by making it a closure.

function setmetatables(t,mts) --takes a table and a list of metatables
  return setmetatable(t,{__index = function(self, k)
    --collisions are resolved in this implementation by simply taking the first one that comes along.
    for i, mt in ipairs(mts) do
      local member = mt[k]
      if member then return member end
    end
  end})
end

camera = {}
mobilephone = {}
cameraphone = setemetatables({},{camera,mobilephone})

M2000 Interpreter

Module CheckIt {
      Class Camera {
      Private:
            cameratype$
      Class:            
            module Camera (.cameratype$){
            }
      }
      \\ INHERITANCE AT CODE LEVEL
      Class MobilePhone {
      Private:
            model$
       Class:
            module  MobilePhone (.model$) {
            }
      }
      Class CameraPhone  as Camera as MobilePhone {
            Module CameraPhone ( .model$, .cameratype$) {
            }
      }
      CP1 =CameraPhone("X-15", "OBSCURE")
      Print CP1 is type CameraPhone = true
      Print CP1 is type Camera = true
      Print CP1 is type MobilePhone = true

      \\ INHERITANCE AT OBJECT LEVEL
      CP2 = MobilePhone("X-9") with Camera("WIDE")
      \\ CP3 has no type
      Group CP3 {
             Module PrintAll {
                   If this is type Camera and this is type MobilePhone then
                         Print .model$, .cameratype$
                   Else
                         Print "Nothing to print"
                   End if
             }
      }
      CP3.PrintAll   ' Nothing to print
      \\ using pointers and prepate inheritance at object level
      CP->(CP1 with CP3)
      CP=>PrintAll
      CP->(CP2 with CP3)
      CP=>PrintAll      
}
CheckIt

Nemerle

Like C#, Nemerle only allows pseudo-multiple inheritance through interfaces. In Nemerle, the base class must be listed before any interfaces.

interface ICamera {
    // ...
}
 
class MobilePhone {
    // ...
}
 
class CameraPhone: MobilePhone, ICamera {
    // ...
}

NetRexx

Like Java, NetRexx doesn't allow true multiple inheritance but instead restricts that capability to interfaces. NetRexx permits the implementation of multiple interfaces. All methods in interfaces are implicitly abstract, thus when you implement an interface you must implement its specified methods.

In this sample the class/interface names are augmented over those required in the task to prevent namespace pollution. The sample also provides a complete working implementation to demonstrate the capability.

/* NetRexx */
options replace format comments java crossref symbols binary

class RInheritMultiple public
  method main(args = String[]) public static
    iPhone = RInheritMultiple_CameraPhone()
    if iPhone <= RInheritMultiple_Camera then -
      say -
      'Object' hashToString(iPhone) '['iPhone.getClass().getSimpleName()']' -
      'is a' RInheritMultiple_Camera.class.getSimpleName()
    if iPhone <= RInheritMultiple_MobilePhone then -
      say -
      'Object' hashToString(iPhone) '['iPhone.getClass().getSimpleName()']' -
      'is a' RInheritMultiple_MobilePhone.class.getSimpleName()
    say iPhone.snap()
    say iPhone.call()
    return
  method hashToString(that = Object) public static
    return '@'(Rexx that.hashCode()).d2x().right(8, 0)

class RInheritMultiple_Camera private interface
  -- properties follow...
  shutter = 'click...'
  -- method prototypes follow
  method snap() public returns Rexx

class RInheritMultiple_MobilePhone private interface
  -- properties follow...
  ringTone = 'ring...'
  -- method prototypes follow
  method call() public returns Rexx

class RInheritMultiple_CameraPhone private -
  implements -
    RInheritMultiple_Camera, -
    RInheritMultiple_MobilePhone -
  uses -
    RInheritMultiple_Camera, -
    RInheritMultiple_MobilePhone
  method RInheritMultiple_CameraPhone() public
    return
  -- method implementations follow 
  method snap() public
    return shutter
  method call() public
    return ringTone

Output:

Object @7F546C85 [RInheritMultiple_CameraPhone] is a RInheritMultiple_Camera
Object @7F546C85 [RInheritMultiple_CameraPhone] is a RInheritMultiple_MobilePhone
click...
ring...

Nim

nim does not support multiple inheritance (version<=1.4.6). It is just a demonstration of the procedure reloading nature of nim code.

type
  Camera = ref object of RootObj
  MobilePhone = ref object of RootObj
  CameraPhone = object
    camera: Camera
    phone: MobilePhone
proc `is`(cp: CameraPhone, t: typedesc): bool =
  for field in cp.fields():
    if field of t:
      return true
var cp: CameraPhone
echo(cp is Camera)
echo(cp is MobilePhone)

Output:

true
true

Objective-C

Like Java, Objective-C does not allow multiple inheritance, but a class can "conform to" multiple protocols. All methods in protocols are abstract (they don't have an implementation). When you conform to a protocol you need to implement the specified methods.

If you simply want to combine the functionality (method implementations) of multiple classes, you can use message forwarding to mimic the functionality of those classes without actually inheriting them, as described in this guide:

@interface Camera : NSObject {
}
@end

@implementation Camera
@end

@interface MobilePhone : NSObject {
}
@end

@implementation MobilePhone
@end

@interface CameraPhone : NSObject {
  Camera *camera;
  MobilePhone *phone;
}
@end

@implementation CameraPhone

-(instancetype)init {
  if ((self = [super init])) {
    camera = [[Camera alloc] init];
    phone = [[MobilePhone alloc] init];
  }
  return self;
}

-(void)forwardInvocation:(NSInvocation *)anInvocation {
  SEL aSelector = [anInvocation selector];
  if ([camera respondsToSelector:aSelector])
    [anInvocation invokeWithTarget:camera];
  else if ([phone respondsToSelector:aSelector])
    [anInvocation invokeWithTarget:phone];
  else
    [self doesNotRecognizeSelector:aSelector];
}

-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
  return [camera methodSignatureForSelector:aSelector]
  ?: [phone methodSignatureForSelector:aSelector]
  ?: [super methodSignatureForSelector:aSelector];
}

-(BOOL)respondsToSelector:(SEL)aSelector {
  return [camera respondsToSelector:aSelector]
  || [phone respondsToSelector:aSelector]
  || [super respondsToSelector:aSelector];  
}

@end

Caveat: the CameraPhone class will still technically not inherit from either the Camera or MobilePhone classes, so testing a CameraPhone object with -isKindOfClass: with the Camera or MobilePhone classes will still fail.

OCaml

class camera =
  object (self)
    (*functions go here...*)
  end

class mobile_phone =
  object (self)
    (*functions go here...*)
  end

class camera_phone =
  object (self)
    inherit camera
    inherit mobile_phone
    (*functions go here...*)
  end

Oforth

Oforth does not implement multiple inheritance. It allows only one parent class.

Oforth implements properties (like Comparable, Indexable, ...). A property can have attributes and methods. A class can have multiple properties.

If Camera and MobilePhone are designed as properties, we can write :

Property new: Camera
Property new: MobilePhone

Object Class new: CameraPhone
CameraPhone is: Camera
CameraPhone is: MobilePhone

ooRexx

ooRexx classes have a single superclass and can inherit from multiple mixins. Mixins are more than just interfaces. They can contain concrete method implementations and also create instance variables (scoped as private variables to the mixin methods).

-- inherited classes must be created as mixinclasses.
::class phone mixinclass object

::class camera mixinclass object

-- not a direct subclass of either, but inherits both
::class cameraphone inherit phone camera

-- could also be
::class cameraphone1 subclass phone inherit camera

-- or

::class cameraphone2 subclass camera inherit phone

OxygenBasic

class Camera
  string cbuf
  method TakePhoto()
  end method
  method ViewPhoto()
  end method
end class

class MobilePhone
  string pbuf
  method MakeCall()
  end method
  method TakeCall()
  end method
end class

class CameraPhone
  has Camera,MobilePhone
end class

CameraPhone cp

cp.ViewPhoto
cp.MakeCall

Oz

class Camera end

class MobilePhone end

class CameraPhone from Camera MobilePhone end

Pascal

See Delphi

Perl

package Camera;
#functions go here...
1;

package MobilePhone;
#functions go here...
1;

package CameraPhone;
use Camera;
use MobilePhone;
@ISA = qw( Camera MobilePhone );
#functions go here...
1;

or

package CameraPhone;
use base qw/Camera MobilePhone/;
#functions go here...

The same using the MooseX::Declare extention:

use MooseX::Declare;

class Camera {
    # methods ...
}
class MobilePhone {
    # methods ...
}
class CameraPhone extends(Camera, MobilePhone) {
    # methods ...
}

Phix

Library: Phix/Class

Needs 0.8.1+

inheritance

The programmer is expected to assume complete responsibility (away from the compiler) for checking/resolving any conflicts.

class Camra
    string name = "nikkon"
end class
class Mobile
--  string name = "nokia" -- oops!
    string mane = "nokia" -- ok!
end class
class CamraPhone extends Camra,Mobile
    procedure show() ?{name,mane} end procedure
end class
CamraPhone cp = new()
cp.show()

Output:

{"nikkon","nokia"}

composition

The programmer is expected to assume complete responsibility for invoking new() appropriately.
The example below shows four different approaches to invoking all the new() that are needed (one pair commented out).
Note that invoking new() inside a class definition creates shared references to a single instance.
The compiler demands to be explicitly told what the inner/inlined new() on cp2 are actually for.

class Camera
    public string name = "nikkon"
end class
class MobilePhone
    public string name = "nokia" -- (clash no more)
end class
class CameraPhone
--  Camera c = new()
--  MobilePhone m = new()
    public Camera c
    public MobilePhone m
    procedure show() ?{c.name,m.name} end procedure
end class
Camera c = new({"canon"})
MobilePhone m = new()
CameraPhone cp1 = new({c,m}),
            cp2 = new({new("Camera"),new("MobilePhone")}),
            cp3 = new() -- (internal/shared/NULL c,m)
cp3.c = new()           -- (obviously c must be public)
cp3.m = new({"LG20"})   --     ""     m    ""     ""
cp1.show()
cp2.show()
cp3.show()      -- crashes without internal/above new()

Output:

{"canon","nokia"}
{"nikkon","nokia"}
{"nikkon","LG20"}

PicoLisp

(class +Camera)
(class +MobilePhone)
(class +CameraPhone +MobilePhone +Camera)

Pop11

;;; load object support
lib objectclass;

define :class Camera;
   ;;; slots go here
enddefine;

define :class MobilePhone;
   ;;; slots go here
enddefine;

define :class CameraPhone is Camera, MobilePhone;
   ;;; extra slots go here
enddefine;

;;; methods go here

PowerShell

Works with: PowerShell version 5

class Camera {}
class MobilePhone {}
class CameraPhone : Camera, MobilePhone {}

PureBasic

Using the open-source precompiler SimpleOOP.

Class Camera
EndClass

Class Mobil
EndClass

Class CameraMobile Extends Camera Extends Mobil
EndClass

Python

class Camera:
  pass #functions go here...

class MobilePhone:
  pass #functions go here...

class CameraPhone(Camera, MobilePhone):
  pass #functions go here...

Racket

Racket allows multiple inheritance with interfaces, but not classes. Mixins can be used to achieve some of the benefits of multiple inheritance.

#lang racket

(define camera<%>       (interface ()))
(define mobile-phone<%> (interface ()))

(define camera-phone%
  (class* object% (camera<%> mobile-phone<%>)
    (super-new)
    ;; implement methods here
    ))

Raku

(formerly Perl 6)

Works with: Rakudo version 2012.06

class Camera {}
class MobilePhone {}
class CameraPhone is Camera is MobilePhone {}

say CameraPhone.^mro;     # undefined type object
say CameraPhone.new.^mro; # instantiated object

Output:

CameraPhone() Camera() MobilePhone() Any() Mu()
CameraPhone() Camera() MobilePhone() Any() Mu()

The .^mro is not an ordinary method call, but a call to the object's metaobject that returns the method resolution order for this type.

Ring

# Project : Inheritance/Multiple

mergemethods(:CameraPhone,:MobilePhone)

o1 = new CameraPhone 
? o1
? o1.testCamera()
? o1.testMobilePhone()

func AddParentClassAttributes oObject,cClass
    # Add Attributes 
        cCode = "oTempObject = new " + cClass 
        eval(cCode)
        for cAttribute in Attributes(oTempObject)
            AddAttribute(oObject,cAttribute)
            cCode = "oObject." + cAttribute + " = oTempObject." + cAttribute
            eval(cCode)
        next 
            

class Camera
    Name = "Camera"
    func testCamera
        ? "Message from testCamera"

class MobilePhone
    Type = "Android"
    func testMobilePhone 
        ? "Message from MobilePhone"

class CameraPhone from Camera 

    # Add MobilePhone Attributes 
        AddParentClassAttributes(self,:MobilePhone)

Output:

name: Camera
type: Android
Message from testCamera
Message from MobilePhone

Ruby

Ruby does not have multiple inheritance, but you can mix modules into classes:

module Camera
  # define methods here
end
class MobilePhone
  # define methods here
end
class CameraPhone < MobilePhone
  include Camera
  # define methods here
end

Rust

trait Camera {}
trait MobilePhone {}
trait CameraPhone: Camera + MobilePhone {}

Scala

trait Camera
trait MobilePhone
class CameraPhone extends Camera with MobilePhone

Self

Self is a class-free, object-oriented language, and as such, it uses prototypal inheritance instead of classical inheritance. This is an example of the relevant excerpts from a Self transporter fileout. Normally the object tree would be built and navigated within the graphical Self environment.

camera = ()

mobilePhone = ()

cameraPhone = (| cameraParent* = camera. mobilePhoneParent* = mobilePhone |)

Sidef

class Camera {};
class MobilePhone {};
class CameraPhone << Camera, MobilePhone {};

Slate

define: #Camera.
define: #MobilePhone.
define: #CameraPhone &parents: {Camera. MobilePhone}.

Swift

Like Objective-C, Swift does not allow multiple inheritance. However, you can conform to multiple protocols.

protocol Camera {
    
}

protocol Phone {
    
}

class CameraPhone: Camera, Phone {
    
}

Tcl

Works with: Tcl version 8.6

or

Library: TclOO

package require TclOO

oo::class create Camera
oo::class create MobilePhone
oo::class create CameraPhone {
    superclass Camera MobilePhone
}

Wren

Wren does not support either multiple inheritance or interfaces.

However, multiple inheritance can be simulated by inheriting from a single class and then embedding objects of other classes and wrapping their methods.

class Camera {
    construct new() {}
    snap() { System.print("taking a photo") }
}

class Phone {
    construct new() {}
    call() { System.print("calling home") }
}

class CameraPhone is Camera {
    construct new(phone) { _phone = phone } // uses composition for the Phone part
    // inherits Camera's snap() method
    // Phone's call() method can be wrapped
    call() { _phone.call() }
}

var p = Phone.new()
var cp = CameraPhone.new(p)
cp.snap()
cp.call()

Output:

taking a photo
calling home

zkl

class Camera{} class MobilePhone{}
class CameraPhone(Camera,MobilePhone){}
CameraPhone.linearizeParents

Output:

Show the class search order

L(Class(CameraPhone),Class(Camera),Class(MobilePhone))