Polymorphism
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You are encouraged to solve this task according to the task description, using any language you may know.
Create two classes Point(x,y) and Circle(x,y,r) with a polymorphic function print, accessors for (x,y,r), copy constructor, assignment and destructor and every possible default constructors
ActionScript
<lang actionscript>package {
public class Point { protected var _x:Number; protected var _y:Number; public function Point(x:Number = 0, y:Number = 0) { _x = x; _y = y; } public function getX():Number { return _x; } public function setX(x:Number):void { _x = x; } public function getY():Number { return _y; } public function setY(y:Number):void { _x = y; } public function print():void { trace("Point"); } }
}</lang> <lang actionscript>package {
public class Circle extends Point { private var r:Number; public function Circle(x:Number=0, y:Number=0, r:Number=0) { super(x, y); this.r = r; } public function getR():Number { return r; } public function setR(r:Number):void { this.r = r; } public override function print():void { trace("Circle"); } }
}</lang>
Ada
This example is constructed using a parent package and a child package. The parent package defines the Point type. The child package defines the Circle type. <lang ada>package Shapes is
type Point is tagged private; procedure Print(Item : in Point); function Setx(Item : in Point; Val : Integer) return Point; function Sety(Item : in Point; Val : Integer) return Point; function Getx(Item : in Point) return Integer; function Gety(Item : in Point) return Integer; function Create return Point; function Create(X : Integer) return Point; function Create(X, Y : Integer) return Point;
private
type Point is tagged record X : Integer := 0; Y : Integer := 0; end record;
end Shapes;</lang> <lang ada>with Ada.Text_Io; use Ada.Text_Io;
package body Shapes is
----------- -- Print -- -----------
procedure Print (Item : in Point) is begin Put_line("Point"); end Print;
---------- -- Setx -- ----------
function Setx (Item : in Point; Val : Integer) return Point is begin return (Val, Item.Y); end Setx;
---------- -- Sety -- ----------
function Sety (Item : in Point; Val : Integer) return Point is begin return (Item.X, Val); end Sety;
---------- -- Getx -- ----------
function Getx (Item : in Point) return Integer is begin return Item.X; end Getx;
---------- -- Gety -- ----------
function Gety (Item : in Point) return Integer is begin return Item.Y; end Gety;
------------ -- Create -- ------------
function Create return Point is begin return (0, 0); end Create;
------------ -- Create -- ------------
function Create (X : Integer) return Point is begin return (X, 0); end Create;
------------ -- Create -- ------------
function Create (X, Y : Integer) return Point is begin return (X, Y); end Create;
end Shapes;</lang> The following is the child package defining the Circle type. <lang ada>package Shapes.Circles is
type Circle is new Point with private; procedure Print(Item : Circle); function Setx(Item : Circle; Val : Integer) return Circle; function Sety(Item : Circle; Val : Integer) return Circle; function Setr(Item : Circle; Val : Integer) return Circle; function Getr(Item : Circle) return Integer; function Create(P : Point) return Circle; function Create(P : Point; R : Integer) return Circle; function Create(X : Integer) return Circle; function Create(X : Integer; Y : Integer) return Circle; function Create(X : Integer; Y : Integer; R : Integer) return Circle; function Create return Circle;
private
type Circle is new Point with record R : Integer := 0; end record;
end Shapes.Circles;</lang> <lang ada>with Ada.Text_Io; use Ada.Text_IO;
package body Shapes.Circles is
----------- -- Print -- -----------
procedure Print (Item : Circle) is begin Put_line("Circle"); end Print;
---------- -- Setx -- ----------
function Setx (Item : Circle; Val : Integer) return Circle is begin return (Val, Item.Y, Item.R); end Setx;
---------- -- Sety -- ----------
function Sety (Item : Circle; Val : Integer) return Circle is Temp : Circle := Item; begin Temp.Y := Val; return Temp; end Sety;
---------- -- Setr -- ----------
function Setr (Item : Circle; Val : Integer) return Circle is begin return (Item.X, Item.Y, Val); end Setr;
---------- -- Getr -- ----------
function Getr (Item : Circle) return Integer is begin return Item.R; end Getr;
------------ -- Create -- ------------
function Create (P : Point) return Circle is begin return (P.X, P.Y, 0); end Create;
------------ -- Create -- ------------
function Create (P : Point; R : Integer) return Circle is begin return (P.X, P.Y, R); end Create;
------------ -- Create -- ------------
function Create (X : Integer) return Circle is begin return (X, 0, 0); end Create;
------------ -- Create -- ------------
function Create (X : Integer; Y : Integer) return Circle is begin return (X, Y, 0); end Create;
------------ -- Create -- ------------
function Create (X : Integer; Y : Integer; R : Integer) return Circle is begin return (X, Y, R); end Create;
------------ -- Create -- ------------
function Create return Circle is begin return (0, 0, 0); end Create;
end Shapes.Circles;</lang> The following procedure is an entry point for a program, serving the same purpose as the main function in C. <lang ada>with Shapes.Circles; use Shapes.Circles; use Shapes;
procedure Shapes_Main is
P : Point; C : Circle;
begin
P.Print; C.Print;
end Shapes_Main;</lang>
Aikido
<lang aikido> class Point (protected x=0.0, protected y=0.0) {
public function print { println ("Point") }
public function getX { return x } public function getY { return y }
public function setX(nx) { x = nx } public function setY(ny) { y = ny }
}
class Circle (x=0.0, y=0.0, r=0.0) extends Point (x, y) {
public function print { println ("Circle") }
public function getR { return r } public function setR(nr) { r = nr }
}
var p = new Point (1, 2) var c = new Circle (1, 2, 3) p.print() c.print()
</lang>
BASIC
BBC BASIC
<lang bbcbasic> INSTALL @lib$ + "CLASSLIB"
REM Create parent class with void 'doprint' method: DIM PrintableShape{doprint} PROC_class(PrintableShape{}) REM Create derived class for Point: DIM Point{x#, y#, setxy, retx, rety, @constructor, @@destructor} PROC_inherit(Point{}, PrintableShape{}) DEF Point.setxy (x,y) : Point.x# = x : Point.y# = y : ENDPROC DEF Point.retx = Point.x# DEF Point.rety = Point.y# DEF Point.@constructor Point.x# = 1.23 : Point.y# = 4.56 : ENDPROC DEF Point.@@destructor : ENDPROC DEF Point.doprint : PRINT Point.x#, Point.y# : ENDPROC PROC_class(Point{}) REM Create derived class for Circle: DIM Circle{x#, y#, r#, setxy, setr, retx, rety, retr, @con, @@des} PROC_inherit(Circle{}, PrintableShape{}) DEF Circle.setxy (x,y) : Circle.x# = x : Circle.y# = y : ENDPROC DEF Circle.setr (r) : Circle.r# = r : ENDPROC DEF Circle.retx = Circle.x# DEF Circle.rety = Circle.y# DEF Circle.retr = Circle.r# DEF Circle.@con Circle.x# = 3.2 : Circle.y# = 6.5 : Circle.r# = 7 : ENDPROC DEF Circle.@@des : ENDPROC DEF Circle.doprint : PRINT Circle.x#, Circle.y#, Circle.r# : ENDPROC PROC_class(Circle{}) REM Test the polymorphic 'doprint' function: PROC_new(mypoint{}, Point{}) PROC(mypoint.doprint) PROC_discard(mypoint{}) PROC_new(mycircle{}, Circle{}) PROC(mycircle.doprint) PROC_discard(mycircle{}) END</lang>
Output:
1.23 4.56 3.2 6.5 7
C
- See Polymorphism/C
C++
<lang cpp>class Point {
protected: int x, y; public: Point(int x0 = 0, int y0 = 0) : x(x0), y(y0) {} Point(const Point& p) : x(p.x), y(p.y) {} virtual ~Point() {} const Point& operator=(const Point& p) { if(this != &p) { x = p.x; y = p.y; } return *this; } int getX() { return x; } int getY() { return y; } int setX(int x0) { x = x0; } int setY(int y0) { y = y0; } virtual void print() { printf("Point\n"); }
};
class Circle : public Point {
private: int r; public: Circle(Point p, int r0 = 0) : Point(p), r(r0) {} Circle(int x0 = 0, int y0 = 0, int r0 = 0) : Point(x0, y0), r(r0) {} virtual ~Circle() {} const Circle& operator=(const Circle& c) { if(this != &c) { x = c.x; y = c.y; r = c.r; } return *this; } int getR() { return r; } int setR(int r0) { r = r0; } virtual void print() { printf("Circle\n"); }
};
int main() {
Point* p = new Point(); Point* c = new Circle(); p->print(); c->print(); return 0;
}</lang>
Pattern: Curiously Recurring Template Pattern
<lang cpp>// CRTP: Curiously Recurring Template Pattern template <typename Derived> class PointShape { protected:
int x, y;
public:
PointShape(int x0, int y0) : x(x0), y(y0) { } ~PointShape() { } int getX() { return x; } int getY() { return y; } int setX(int x0) { x = x0; } int setY(int y0) { y = y0; }
// compile-time virtual function void print() { reinterpret_cast<const Derived*>(this)->printType(); }
};
class Point : public PointShape<Point> { public:
Point(int x0 = 0, int y0 = 0) : PointShape(x0, y0) { } Point(const Point& p) : PointShape(p.x, p.y) { } ~Point() {} const Point& operator=(const Point& p) { if(this != &p) { x = p.x; y = p.y; } return *this; } void printType() { printf("Point\n"); }
};
class Circle : public PointShape<Circle> { private:
int r;
public:
Circle(int x0 = 0, int y0 = 0, int r0 = 0) : PointShape(x0, y0), r(r0) { } Circle(Point p, int r0 = 0) : PointShape(p.x, p.y), r(r0) { } ~Circle() {} const Circle& operator=(const Circle& c) { if(this != &c) { x = c.x; y = c.y; r = c.r; } return *this; } int getR() { return r; } int setR(int r0) { r = r0; } void printType() { printf("Circle\n"); }
};
int main() {
Point* p = new Point(); Point* c = new Circle(); p->print(); c->print(); return 0;
}</lang>
C#
<lang csharp>using System; class Point {
protected int x, y; public Point() : this(0) {} public Point(int x) : this(x,0) {} public Point(int x, int y) { this.x = x; this.y = y; } public int X { get { return x; } set { x = value; } } public int Y { get { return y; } set { y = value; } } public virtual void print() { System.Console.WriteLine("Point"); }
}
public class Circle : Point {
private int r; public Circle(Point p) : this(p,0) { } public Circle(Point p, int r) : base(p) { this.r = r; } public Circle() : this(0) { } public Circle(int x) : this(x,0) { } public Circle(int x, int y) : this(x,y,0) { } public Circle(int x, int y, int r) : base(x,y) { this.r = r; } public int R { get { return r; } set { r = value; } } public override void print() { System.Console.WriteLine("Circle"); } public static void main(String args[]) { Point p = new Point(); Point c = new Circle(); p.print(); c.print(); }
}</lang>
Clojure
Clojure 1.2.
<lang lisp>(defprotocol Printable
(print-it [this] "Prints out the Printable."))
(deftype Point [x y]
Printable (print-it [this] (println (str "Point: " x " " y))))
(defn create-point
"Redundant constructor function." [x y] (Point. x y))
(deftype Circle [x y r]
Printable (print-it [this] (println (str "Circle: " x " " y " " r))))
(defn create-circle
"Redundant consturctor function." [x y r] (Circle. x y r))</lang>
Common Lisp
<lang lisp>(defclass point ()
((x :initarg :x :initform 0 :accessor x) (y :initarg :y :initform 0 :accessor y)))
(defclass circle (point)
((radius :initarg :radius :initform 0 :accessor radius)))
(defgeneric shallow-copy (object)) (defmethod shallow-copy ((p point))
(make-instance 'point :x (x p) :y (y p)))
(defmethod shallow-copy ((c circle))
(make-instance 'circle :x (x c) :y (y c) :radius (radius c)))
(defgeneric print-shape (shape)) (defmethod print-shape ((p point))
(print 'point))
(defmethod print-shape ((c circle))
(print 'circle))
(let ((p (make-instance 'point :x 10))
(c (make-instance 'circle :radius 5))) (print-shape p) (print-shape c))</lang>
D
<lang d>import std.stdio: writeln;
class Point {
private int x, y; this(int x_=0, int y_=0) { x = x_; y = y_; } this(Point p_) { x = p_.getX(); y = p_.getY(); } int getX() { return x; } void setX(int x_) { this.x = x_; } int getY() { return y; } void setY(int y_) { this.y = y_; }
}
class Circle : Point {
private int r; this(int x_=0, int y_=0, int r_=0) { super(x_, y_); r = r_; } this(Point p, int r_=0) { super(p); r = r_; } this(Circle c_) { super(c_.getX(), c_.getY()); r = c_.getR(); } int getR() { return r; } void setR(int r0) { this.r = r0; }
}
void main() {
auto p = new Point(); auto c = new Circle(); writeln(p); writeln(c);
}</lang>
Delphi
<lang delphi>type
{ TPoint }
TMyPoint = class private FX: Integer; FY: Integer; public constructor Create; overload; constructor Create(X0: Integer; Y0: Integer); overload; constructor Create(MyPoint: TMyPoint); overload; destructor Destroy; override;
procedure Print; virtual;
property X: Integer read FX write FX; property Y: Integer read FY write FY; end;
{ TCircle }
TCircle = class(TMyPoint) private FR: Integer; public constructor Create(X0: Integer; Y0: Integer; R0: Integer); overload; constructor Create(MyPoint: TMyPoint; R0: Integer); overload; constructor Create(Circle: TCircle); overload; destructor Destroy; override;
procedure Print; override;
property R: Integer read FR write FR; end;
implementation
uses Dialogs;
{ TCircle }
constructor TCircle.Create(X0: Integer; Y0: Integer; R0: Integer); begin
inherited Create(X0, Y0); FR := R0;
end;
constructor TCircle.Create(MyPoint: TMyPoint; R0: Integer); begin
inherited Create(MyPoint); FR := R0;
end;
constructor TCircle.Create(Circle: TCircle); begin
Create; if not(Circle = Self) then begin FX := Circle.X; FY := Circle.Y; FR := Circle.R; end;
end;
destructor TCircle.Destroy; begin
inherited Destroy;
end;
procedure TCircle.Print; begin
ShowMessage('Circle');
end;
{ TMyPoint }
constructor TMyPoint.Create; begin
inherited Create;
end;
constructor TMyPoint.Create(X0: Integer; Y0: Integer); begin
Create; FX := X0; FY := Y0;
end;
constructor TMyPoint.Create(MyPoint: TMyPoint); begin
Create; if not(MyPoint = Self) then begin FX := MyPoint.X; FY := MyPoint.Y; end;
end;
destructor TMyPoint.Destroy; begin
inherited Destroy;
end;
procedure TMyPoint.Print; begin
ShowMessage('MyPoint');
end;</lang>
<lang delphi>var
MyPoint: TMyPoint; Circle: TCircle;
begin
MyPoint := TMyPoint.Create; try MyPoint.Print; Circle := TCircle.Create; try Circle.Print; finally FreeAndNil(Circle); end; finally FreeAndNil(MyPoint); end;
end;</lang>
E
<lang e>def makePoint(x, y) {
def point implements pbc { to __printOn(out) { out.print(`<point $x,$y>`) } to __optUncall() { return [makePoint, "run", [x, y]] } to x() { return x } to y() { return y } to withX(new) { return makePoint(new, y) } to withY(new) { return makePoint(x, new) } } return point
}
def makeCircle(x, y, r) {
def circle extends makePoint(x, y) implements pbc { to __printOn(out) { out.print(`<circle $x,$y r $r>`) } to __optUncall() { return [makeCircle, "run", [x, y, r]] } to r() { return r } to withX(new) { return makeCircle(new, y, r) } to withY(new) { return makeCircle(x, new, r) } to withR(new) { return makeCircle(x, y, new) } } return circle
}</lang>
(It is unidiomatic to have mutation operations on an object of this sort in E, so this example has variation operations instead. __optUncall is used for serialization, and is the closest analogue to a copy constructor. E does not have destructors, but only post-mortem finalizers (which are registered after the object is created). The "extends" is only implementation inheritance; it is not necessary to enable polymorphism.)
<lang e>def p := makePoint(0.5, 0.5) def c := makeCircle(1, 1, 2) println(p) println(c)</lang>
Eiffel
<lang eiffel >class
POINT
inherit
ANY redefine out end
create
make, make_origin
feature -- Initialization
make (a_x, a_y: INTEGER) -- Create with values `a_x' and `a_y' do set_x (a_x) set_y (a_y) ensure x_set: x = a_x y_set: y = a_y end
make_origin -- Create at origin do ensure x_set: x = 0 y_set: y = 0 end
feature -- Access
x: INTEGER assign set_x -- Horizontal axis coordinate
y: INTEGER assign set_y -- Vertical axis coordinate
feature -- Element change
set_x (a_x: INTEGER) -- Set `x' coordinate to `a_x' do x := a_x ensure x_set: x = a_x end
set_y (a_y: INTEGER) -- Set `y' coordinate to `a_y' do y := a_y ensure y_set: y = a_y end
feature -- Output
out: STRING -- Display as string do Result := "Point: x = " + x.out + " y = " + y.out end
end</lang>
<lang eiffel >class
CIRCLE
inherit
POINT rename make as point_make redefine make_origin, out end
create
make, make_origin, make_from_point
feature -- Initialization
make (a_x, a_y, a_r: INTEGER) -- Create with values `a_x' and `a_y' and `a_r' require non_negative_radius_argument: a_r >= 0 do point_make (a_x, a_y) set_r (a_r) ensure x_set: x = a_x y_set: y = a_y r_set: r = a_r end
make_origin -- Create at origin with zero radius do Precursor ensure then r_set: r = 0 end
make_from_point (a_p: POINT; a_r: INTEGER) -- Initialize from `a_r' with radius `a_r'. require non_negative_radius_argument: a_r >= 0 do set_x (a_p.x) set_y (a_p.y) set_r (a_r) ensure x_set: x = a_p.x y_set: y = a_p.y r_set: r = a_r end
feature -- Access
r: INTEGER assign set_r -- Radius
feature -- Element change
set_r (a_r: INTEGER) -- Set radius (`r') to `a_r' require non_negative_radius_argument: a_r >= 0 do r := a_r ensure r_set: r = a_r end
feature -- Output
out: STRING -- Display as string do Result := "Circle: x = " + x.out + " y = " + y.out + " r = " + r.out end
invariant
non_negative_radius: r >= 0
end</lang>
<lang eiffel >class
APPLICATION
create
make
feature {NONE} -- Initialization
make -- Run application. local my_point: POINT my_circle: CIRCLE do create my_point.make_origin print (my_point.out + "%N")
create {CIRCLE} my_point.make_origin print (my_point.out + "%N")
create my_point.make (10, 15) print (my_point.out + "%N")
create {CIRCLE} my_point.make (20, 25, 5) print (my_point.out + "%N")
create my_circle.make (30, 35, 10) print (my_circle.out + "%N")
create my_circle.make_from_point (my_point, 35) print (my_circle.out + "%N") end
end</lang>
Output:
<lang text> Point: x = 0 y = 0 Circle: x = 0 y = 0 r = 0 Point: x = 10 y = 15 Circle: x = 20 y = 25 r = 5 Circle: x = 30 y = 35 r = 10 Circle: x = 20 y = 25 r = 35 </lang>
Notes:
The Eiffel example varies slightly from the problem description. The polymorphic feature is out
rather than print
. Both out
and print
are inherited by every Eiffel class from class ANY
. However, it is customary in Eiffel to redefine the query out
to provide a string describing an instance, versus redefining print
. So, this example is written to reflect the Eiffel convention.
Ela
Solution of this problem in Ela is similar to Haskell, as soon as Ela shares with Haskell the same features - namely, classes (typeclasses) and algebraic types.
<lang ela>type Point = Point x y
instance Show Point where
showf _ (Point x y) = "Point " ++ (show x) ++ " " ++ (show y)
instance Name Point where
getField nm (Point x y) | nm == "x" = x | nm == "y" = y | else = fail "Undefined name." isField nm _ = nm == "x" or nm == "y"
pointX = flip Point 0
pointY = Point 0
pointEmpty = Point 0 0
type Circle = Circle x y z
instance Show Circle where
showf _ (Circle x y z) = "Circle " ++ (show x) ++ " " ++ (show y) ++ " " ++ (show z)
instance Name Circle where
getField nm (Circle x y z) | nm == "x" = x | nm == "y" = y | nm == "z" = z | else = fail "Undefined name." isField nm _ = nm == "x" or nm == "y" or nm == "z"
circleXZ = flip Circle 0
circleX x = Circle x 0 0
circleYZ = Circle 0
circleY y = Circle 0 y 0
circleZ = Circle 0 0
circleEmpty = Circle 0 0 0
circleX 1 2</lang>
Class Show is defined in prelude and is effectively an abstraction for all "printable" entities.
Normally, algebraic types are analyzed using pattern matching, however, it is possible to provide a support for an "accessor style" approach by providing an instance for class Name (which is also defined in prelude). With this instance it is possible to write code like so:
<lang ela>c = circleX 12 c.x //Evaluates to 12</lang>
Factor
<lang factor>QUALIFIED: io ! there already is print in io
GENERIC: print ( shape -- )
TUPLE: point x y ; C: <point> point ! shorthand constructor definition
M: point print drop "Point" io:print ;
TUPLE: circle radius x y ; C: <circle> circle
M: circle print drop "Circle" io:print ;</lang>
Forth
There are numerous, mutually incompatible object oriented frameworks for Forth. This one works with the FOOS preprocessor extension of 4tH. Variadic functions in Forth are usually implemented by passing the number of parameters. Since it is highly unlikely that objects are allocated that low in memory it works. Note that X, Y and Z are passed in reverse order, which is quite common for any Forth program. <lang forth>include lib/memcell.4th include 4pp/lib/foos.4pp
- Point ( xn n a--)
class field: x \ x coordinate field: y \ y coordinate method: print \ print routine method: setx \ set x coordinate method: sety \ set y coordinate method: getx \ get x coordinate method: gety \ get y coordinate end-class { \ bind the methods immediately :method { this -> x ! } ; defines setx :method { this -> y ! } ; defines sety :method { this -> x @ } ; defines getx :method { this -> y @ } ; defines gety \ because we'll use them immediately :method { \ e.g. in this print routine ." Point(" this => getx 0 .r ." ," this => gety 0 .r ." )" cr } ; defines print \ and this initialization \ object or argument count dup type@ this type@ = \ if it is an object, a point if \ get the coordinates and set them dup => getx this => setx => gety this => sety else \ otherwise initialize it 0 dup this => setx this => sety case \ and check the argument count 1 of this => setx endof \ one argument : x only 2 of this => setx \ two arguments: x and y this => sety endof endcase then
private{ x y } \ make x and y private }
- Circle ( xn n a --)
over >r ( arg-count object-addr) extends Point \ save the argument count!! field: r \ radius method: getr \ get radius method: setr \ set radius end-extends r> swap { \ retrieve count \ bind the methods immediately :method { this -> r ! } ; defines setr :method { this -> r @ } ; defines getr \ because we'll use them immediately :method { \ e.g. in this print routine ." Circle(" this => getx 0 .r ." ," this => gety 0 .r ." ," this => getr 0 .r ." )" cr } ; defines print \ and this initialization \ object or argument count dup type@ this type@ = \ if it is an object, a circle if \ get the coordinates and set them dup => getx this => setx dup => gety this => sety => getr this => setr else \ otherwise initialize it 0 this => setr case \ and check the argument count 3 of this => setr \ three arguments: x, y and r this => sety \ note the rest is already set this => setx endof \ by "Point" and r was left on endcase \ the stack! then
private{ r } }
0 new Point Point1 Point1 => print 45 23 2 new Point Point2 Point2 => print Point2 new Point Point3 Point3 => print 78 1 new Point Point4 Point4 => print 10 45 23 3 new Circle Circle1 Circle1 => print Point2 new Circle Circle2 Circle2 => print Circle1 new Circle Circle3 Circle3 => print</lang>
Fortran
Fortran provides OO features with the type mechanism. This example works with the Intel 11.1.069 compiler. <lang fortran> module geom
type point real(8), private :: x = 0 real(8), private :: y = 0 contains procedure, public :: get_x procedure, public :: get_y procedure, public :: set_x procedure, public :: set_y procedure, public :: print => print_point end type point
type, extends(point) :: circle real(8), private :: r = 0 contains procedure, public :: get_r procedure, public :: set_r procedure, public :: print => print_circle end type circle
contains
real(8) function get_x(this) class(point), intent(in) :: this get_x = this%x end function get_x
real(8) function get_y(this) class(point), intent(in) :: this get_y = this%y end function get_y
subroutine set_x(this, val) class(point), intent(inout) :: this real(8), intent(in) :: val this%x = val end subroutine set_x
subroutine set_y(this, val) class(point), intent(inout) :: this real(8), intent(in) :: val this%y = val end subroutine set_y
subroutine print_point(this) class(point), intent(in) :: this write(*,'(2(a,f0.4),a)') 'Point(',this%x,', ',this%y,')' end subroutine print_point
real(8) function get_r(this) class(circle), intent(in) :: this get_r = this%r end function get_r
subroutine set_r(this, val) class(circle), intent(inout) :: this real(8), intent(in) :: val this%r = val end subroutine set_r
subroutine print_circle(this) class(circle), intent(in) :: this write(*,'(3(a,f0.4),a)') 'Circle(',this%x,', ',this%y,'; ',this%r,')' end subroutine print_circle
end module geom
program inh
use geom
type(point) :: p type(circle) :: c
p = point(2.0d0, 3.0d0) call p%print
c = circle(3.0d0, 4.0d0, 5.0d0) call c%print
end program inh
</lang>
F#
Polymorphism is achieved by defining an interface Printable
which is implemented by Point
and Circle
. (In real code, you should override the ToString
method which every class inherits from Object
.)
Due to the use of optional parameters, we only need one constructor for every class. No accessors are necessary because we use public read-only properties. (Mutable properties are possible, too, but should be avoided in idiomatic code.)
<lang fsharp>type Printable =
abstract member Print : unit -> unit
type Point(?x, ?y) =
member t.x = defaultArg x 0.0 member t.y = defaultArg y 0.0 interface Printable with member t.Print() = printfn "Point(x:%f, y:%f)" t.x t.y
type Circle(?center, ?radius) =
member t.center = defaultArg center (new Point()) member t.radius = defaultArg radius 1.0 interface Printable with member t.Print() = printfn "Circle(x:%f, y:%f, r:%f)" t.center.x t.center.y t.radius</lang>
Go
<lang go>package main
import "fmt"
type point struct {
x, y float64
}
type circle struct {
x, y, r float64
}
type printer interface {
print()
}
func (p *point) print() {
fmt.Println(p.x, p.y)
}
func (c *circle) print() {
fmt.Println(c.x, c.y, c.r)
}
func main() {
var i printer // polymorphic variable i = newPoint(3, 4) // assign one type i.print() // call polymorphic function i = newCircle(5, 12, 13) // assign different type to same variable i.print() // same call accesses different method now.
}
// Above is a sort of polymorphism: both types implement the printer // interface. The print function can be called through a variable // of type printer, without knowing the underlying type.
// Below is other stuff the task asks for. Note that none of it is // needed for cases as simple as this task, and it is not idomatic // to write any of these functions in these simple cases.
// Accessors are not idiomatic in Go. Instead, simply access struct // fields directly. To allow access from another package, you "export" // the field by capitalizing the field name. func (p *point) getX() float64 { return p.x } func (p *point) getY() float64 { return p.y } func (p *point) setX(v float64) { p.x = v } func (p *point) setY(v float64) { p.y = v }
func (c *circle) getX() float64 { return c.x } func (c *circle) getY() float64 { return c.y } func (c *circle) getR() float64 { return c.r } func (c *circle) setX(v float64) { c.x = v } func (c *circle) setY(v float64) { c.y = v } func (c *circle) setR(v float64) { c.r = v }
// Copy constructors, not idiomatic. Structs are assignable so // you can simply declare and assign them as needed. func (p *point) clone() *point { r := *p; return &r } func (c *circle) clone() *circle { r := *c; return &r }
// Assignment methods, not idiomatic. Just use the assignment operator. func (p *point) set(q *point) { *p = *q } func (c *circle) set(d *circle) { *c = *d }
// Constructors are idiomatic only when construction involves something // more than just assigning initial values. By default, structs // are created as "zero values," that is, with all fields zero, // empty, or nil. The struct literal synax allows for all fields to // initialized, or for any subset of fields to be initialized by name. // These feautures take the place of trivial default constructors. // When additional initialization is needed, it is conventional to // name a function New, New<Type>, or within a package, new<Type> // as shown here. func newPoint(x, y float64) *point {
return &point{x, y}
} func newCircle(x, y, r float64) *circle {
return &circle{x, y, r}
}
// Destructors are never used in Go. Objects are garbage collected.</lang>
Haskell
Polymorphism is achieved through the type class Show
<lang haskell>data Point = Point Integer Integer instance Show Point where
show (Point x y) = "Point at "++(show x)++","++(show y)
-- Constructor that sets y to 0 ponXAxis = flip Point 0
-- Constructor that sets x to 0 ponYAxis = Point 0
-- Constructor that sets x and y to 0 porigin = Point 0 0
data Circle = Circle Integer Integer Integer instance Show Circle where
show (Circle x y r) = "Circle at "++(show x)++","++(show y)++" with radius "++(show r)
-- Constructor that sets y to 0 conXAxis = flip Circle 0
-- Constructor that sets x to 0 conYAxis = Circle 0
-- Constructor that sets x and y to 0 catOrigin = Circle 0 0
--Constructor that sets y and r to 0 c0OnXAxis = flip (flip Circle 0) 0
--Constructor that sets x and r to 0 c0OnYAxis = flip (Circle 0) 0</lang>
Icon and Unicon
This is Unicon specific, as Unicon has classes, but Icon does not.
There is no destructor, as Unicon manages object destruction itself. The copy constructor is emulated by a method. Notice the 'initially' clauses. These act like constructors, in that they accept input parameters during instance construction. These parameters are null if not used, and so the initial field values are set to 0 if the entered value is null (tested using the '/' symbol).
<lang Unicon>class Circle (x, y, r)
# make a new copy of this instance method copy () return Circle (x, y, r) end
# print a representation of this instance method print () write ("Circle (" || x || ", " || y || ", " || r || ")") end
# called during instance construction, to pass in field values initially (x, y, r) self.x := if /x then 0 else x # set to 0 if argument not present self.y := if /y then 0 else y self.r := if /r then 0 else r
end
class Point (x, y)
# make a new copy of this instance method copy () return Point (x, y) end
# print a representation of this instance method print () write ("Point (" || x || ", " || y || ")") end
# called during instance construction, to pass in field values initially (x, y) self.x := if /x then 0 else x # set to 0 if argument not present self.y := if /y then 0 else y
end
procedure main ()
p1 := Point () p2 := Point (1) p3 := Point (1,2) p4 := p3.copy ()
write ("Points:") p1.print () p2.print () p3.print () p4.print () # demonstrate field mutator/accessor p3.x := 3 write ("p3 value of x is: " || p3.x)
c1 := Circle () c2 := Circle (1) c3 := Circle (1,2) c4 := Circle (1,2,3)
write ("Circles:") c1.print () c2.print () c3.print () c4.print ()
end </lang>
Inform 7
Accessors are not needed since property values are public. Constructors and destructors are not needed since objects are statically allocated and initialized.
<lang inform7>Space is a room.
A point is a kind of thing. A point has a number called X position. A point has a number called Y position.
A circle is a kind of point. A circle has a number called radius.
To print (P - point): say "Point: [X position of P], [Y position of P]." To print (C - circle): say "Circle: [X position of C], [Y position of C] radius [radius of C]."
The origin is a point with X position 0 and Y position 0. The circle of power is a circle with X position 100, Y position 25, radius 7.
When play begins: print the origin; print the circle of power; end the story.</lang>
J
<lang J>coclass 'Point' create=: monad define
'X Y'=:2{.y
) getX=: monad def 'X' getY=: monad def 'Y' setX=: monad def 'X=:y' setY=: monad def 'Y=:y' print=: monad define
smoutput 'Point ',":X,Y
) destroy=: codestroy</lang>
<lang J>coclass 'Circle' coinsert 'Point' create=: monad define
'X Y R'=: 3{.y
) getR=: monad def 'R' setR=: monad def 'R=:y' print=: monad define
smoutput 'Circle ',":X,Y,R
)</lang>
Java
<lang java>class Point {
protected int x, y; public Point() { this(0); } public Point(int x0) { this(x0, 0); } public Point(int x0, int y0) { x = x0; y = y0; } public Point(Point p) { this(p.x, p.y); } public int getX() { return x; } public int getY() { return y; } public int setX(int x0) { x = x0; } public int setY(int y0) { y = y0; } public void print() { System.out.println("Point"); }
}
public class Circle extends Point {
private int r; public Circle(Point p) { this(p, 0); } public Circle(Point p, int r0) { super(p); r = r0; } public Circle() { this(0); } public Circle(int x0) { this(x0, 0); } public Circle(int x0, int y0) { this(x0, y0, 0); } public Circle(int x0, int y0, int r0) { super(x0, y0); r = r0; } public Circle(Circle c) { this(c.x, c.y, c.r); } public int getR() { return r; } public int setR(int r0) { r = r0; } public void print() { System.out.println("Circle"); } public static void main(String args[]) { Point p = new Point(); Point c = new Circle(); p.print(); c.print(); }
}</lang>
JavaScript
<lang javascript>/* create new Point in one of these ways:
* var p = new Point(x,y); * var p = new Point(a_point); * default value for x,y is 0 */
function Point() {
var arg1 = arguments[0]; var arg2 = arguments[1];
if (arg1 instanceof Point) { this.x = arg1.x; this.y = arg1.y; } else { this.x = arg1 == null ? 0 : arg1; this.y = arg2 == null ? 0 : arg1; }
this.set_x = function(_x) {this.x = _x;} this.set_y = function(_y) {this.y = _y;}
}
Point.prototype.print = function() {
var out = "Point(" + this.x + "," + this.y + ")"; print(out);
}
/* create new Circle in one of these ways:
* var c = new Circle(x,y,r); * var c = new Circle(a_circle); * var c = new Circle(a_point,r); * default value for x,y,r is 0 */
function Circle() {
var arg1 = arguments[0]; var arg2 = arguments[1]; var arg3 = arguments[2];
if (arg1 instanceof Circle) { this.x = arg1.x; this.y = arg1.y; this.r = arg1.r; } else if (arg1 instanceof Point) { this.x = arg1.x; this.y = arg1.y; this.r = arg2 == null ? 0 : arg2; } else { this.x = arg1 == null ? 0 : arg1; this.y = arg2 == null ? 0 : arg2; this.r = arg3 == null ? 0 : arg3; }
this.set_x = function(_x) {this.x = _x;} this.set_y = function(_y) {this.y = _y;} this.set_r = function(_r) {this.r = _r;}
}
Circle.prototype.print = function() {
var out = "Circle(" + this.x + "," + this.y + "," + this.r + ")"; print(out);
}</lang>
Lua
Lua does not have a standard definition of objects or classes, so a basic and typical protoctype-based OOP model will be used. In Lua all objects are tables, and through the use of metatables, polymorphism can be achieved in many ways, this is only one of them. <lang Lua>-- Point local Point = {x = 0, y = 0}
function Point:new(o)
o = o or {} setmetatable(o, self) self.__index = self return o
end
function Point:print()
print("Point(" .. self.x .. ", " .. self.y .. ")")
end
function Point:copy()
return Point:new{x = self.x, y = self.y}
end
-- Circle local Circle = Point:new() Circle.r = 0
function Circle:print()
print("Circle(" .. self.x .. ", " .. self.y .. ", " .. self.r .. ")")
end
function Circle:copy()
return Circle:new{x = self.x, y = self.y, r = self.r}
end</lang>
NetRexx
Note: Based on default values in method prototypes, NetRexx will automatically generate intermediate constructors and methods, thus ensuring that none are omitted. <lang NetRexx>/* NetRexx */
options replace format comments java crossref savelog symbols binary
-- ----------------------------------------------------------------------------- class RCPolymorphism public final
method main(args = String[]) public constant
parry = [Point - Point() - , Point(1.0) - , Point(1.0, 2.0) - , Point(Point(0.3, 0.2)) - , Circle() - , Circle(2.0, 2.0) - , Circle(5.0, 6.0, 7.0) - , Circle(Point(8.0, 9.0)) - , Circle(Point(8.0, 9.0), 4.0) - , Circle(Circle(1.5, 1.4, 1.3)) - ]
loop pp = 0 to parry.length - 1 parry[pp].print end pp
return
-- ----------------------------------------------------------------------------- class RCPolymorphism.Point public binary
properties private
x = double y = double className = Point.class.getSimpleName
method Point(x_ = double 0.0, y_ = double 0.0)
setX(x_) setY(y_) return
method Point(p = Point)
this(p.getX, p.getY) return
method display public returns String
hx = '@'Rexx(Integer.toHexString(hashCode())).right(8, 0) str = Rexx(className).left(10)':'hx': (x,y) = (' || - Rexx(getX()).format(null, 3)',' - Rexx(getY()).format(null, 3)')' return str
method getX public returns double
return x
method getY public returns double
return y
method setX(x_ = double 0.0) inheritable
x = x_ return
method setY(y_ = double 0.0) inheritable
y = y_ return
method print inheritable
say display return
-- ----------------------------------------------------------------------------- class RCPolymorphism.Circle public extends RCPolymorphism.Point binary
properties private
r = double className = Circle.class.getSimpleName
method Circle(x_ = double 0.0, y_ = double 0.0, r_ = double 0.0)
super(x_, y_) setR(r_) return
method Circle(p_ = RCPolymorphism.Point, r_ = double 0.0)
this(p_.getX, p_.getY, r_) return
method Circle(c_ = Circle)
this(c_.getX, c_.getY, c_.getR) return
method getR public returns double
return r
method setR(r_ = double 0.0) inheritable
r = r_ return
method display public returns String
hx = '@'Rexx(Integer.toHexString(hashCode())).right(8, 0) str = Rexx(className).left(10)':'hx': (x,y,r) = (' || - Rexx(getX()).format(null, 3)',' - Rexx(getY()).format(null, 3)',' - Rexx(getR()).format(null, 3)')' return str
</lang>
- Output
Point :@0eb42cbf: (x,y) = (0.000, 0.000) Point :@17dfafd1: (x,y) = (1.000, 0.000) Point :@3343c8b3: (x,y) = (1.000, 2.000) Point :@272d7a10: (x,y) = (0.300, 0.200) Circle :@1aa8c488: (x,y,r) = (0.000, 0.000, 0.000) Circle :@3dfeca64: (x,y,r) = (2.000, 2.000, 0.000) Circle :@22998b08: (x,y,r) = (5.000, 6.000, 7.000) Circle :@0e76cbf7: (x,y,r) = (8.000, 9.000, 0.000) Circle :@1948cc8c: (x,y,r) = (8.000, 9.000, 4.000) Circle :@7a6d084b: (x,y,r) = (1.500, 1.400, 1.300)
Objeck
<lang objeck> bundle Default {
class Point { @x : Int; @y : Int;
New() { @x := 0; @y := 0; }
New(x : Int, y : Int) { @x := x; @y := y; }
New(p : Point) { @x := p->GetX(); @y := p->GetY(); }
method : public : GetX() ~ Int { return @x; } method : public : GetY() ~ Int { return @y; }
method : public : SetX(x : Int) ~ Nil { @x := x; } method : public : SetY(y : Int) ~ Nil { @y := y; }
method : public : Print() ~ Nil { "Point"->PrintLine(); } } class Circle from Point { @r : Int;
New() { Parent(); @r := 0; }
New(p : Point) { Parent(p); @r := 0; } New(c : Circle) { Parent(c->GetX(), c->GetY()); @r := c->GetR(); } method : public : GetR() ~ Int { return @r; }
method : public : SetR(r : Int) ~ Nil { @r := r; }
method : public : Print() ~ Nil { "Circle"->PrintLine(); } } class Poly { function : Main(args : String[]) ~ Nil { p := Point->New(); c := Circle->New(); p->Print(); c->Print(); } }
} </lang>
Objective-C
<lang objc>#import <Foundation/Foundation.h>
@interface RCPoint : NSObject {
int x, y;
} -(id)initWithX:(int)x0; -(id)initWithX:(int)x0 andY:(int)y0; -(id)initWithPoint:(RCPoint *)p; @property (nonatomic) int x; @property (nonatomic) int y; @end
@implementation RCPoint @synthesize x, y; -(id)initWithX:(int)x0 { return [self initWithX:x0 andY:0]; } -(id)initWithX:(int)x0 andY:(int)y0 {
if ((self = [super init])) { x = x0; y = y0; } return self;
} -(id)initWithPoint:(RCPoint *)p { return [self initWithX:p.x andY:p.y]; } -(NSString *)description { return [NSString stringWithFormat:@"<RCPoint %p x: %d y: %d>", self, x, y]; } @end
@interface RCCircle : RCPoint {
int r;
} -(id)initWithCenter:(RCPoint *)p andRadius:(int)r0; -(id)initWithX:(int)x0 andY:(int)y0 andRadius:(int)r0; -(id)initWithCircle:(RCCircle *)c; @property (nonatomic) int r; @end
@implementation RCCircle @synthesize r; -(id)initWithCenter:(RCPoint *)p andRadius:(int)r0 {
if ((self = [super initWithPoint:p])) { r = r0; } return self;
} -(id)initWithX:(int)x0 andY:(int)y0 andRadius:(int)r0 {
if ((self = [super initWithX:x0 andY:y0])) { r = r0; } return self;
} -(id)initWithCircle:(RCCircle *)c { return [self initWithX:c.x andY:c.y andRadius:c.r]; } -(NSString *)description { return [NSString stringWithFormat:@"<RCCircle %p x: %d y: %d r: %d>", self, x, y, r]; } @end
int main(int argc, const char *argv[]) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSLog(@"%@", [[[RCPoint alloc] init] autorelease]); NSLog(@"%@", [[[RCPoint alloc] initWithX:3] autorelease]); NSLog(@"%@", [[[RCPoint alloc] initWithX:3 andY:4] autorelease]); NSLog(@"%@", [[[RCCircle alloc] init] autorelease]); NSLog(@"%@", [[[RCCircle alloc] initWithX:3] autorelease]); NSLog(@"%@", [[[RCCircle alloc] initWithX:3 andY:4] autorelease]); NSLog(@"%@", [[[RCCircle alloc] initWithX:3 andY:4 andRadius:7] autorelease]); RCPoint *p = [[[RCPoint alloc] initWithX:1 andY:2] autorelease]; NSLog(@"%@", [[[RCCircle alloc] initWithPoint:p] autorelease]); NSLog(@"%@", [[[RCCircle alloc] initWithCenter:p andRadius:7] autorelease]); NSLog(@"%d", p.x); // 1 p.x = 8; NSLog(@"%d", p.x); // 8 [pool release]; return 0;
}</lang>
OCaml
<lang ocaml>class point ?(x=0.0) ?(y=0.0) () = (* extra () used to erase the optional parameters *) object (self)
val mutable x = x val mutable y = y
method x = x method y = y method set_x x' = x <- x' method set_y y' = y <- y' method print = Printf.sprintf "Point (%f, %f)" x y method copy = {< >}
end
class circle ?(r=1.0) ?(x=0.0) ?(y=0.0) () = object (self)
inherit point ~x:x ~y:y () val mutable r = r
method r = r method set_r r' = r <- r' method print = Printf.sprintf "Circle (%f, %f, %f)" r x y
end
let print x = print_endline x#print
let () =
let p = new point () in let c = new circle () in print c; print p; c#set_x 10.0; print c; print (new point ~y:2.1 ())</lang>
ooRexx
ooRexx supports traditional class-based polymorphism. The polymorphic methods can be part of the main class sequence or brought in using mixins for multiple inheritance situations. Here is a simple example using point and circle classes in a hierarchy.
<lang ooRexx> p = .point~new(3,2) c = .circle~new(,2,6)
p~print c~print
- class point
- method init
expose x y use strict arg x = 0, y = 0 -- defaults to 0 for any non-specified coordinates
- attribute x
- attribute y
- method print
expose x y say "A point at location ("||x","y")"
- class circle subclass point
- method init
expose radius use strict arg x = 0, y = 0, radius = 0 self~init:super(x, y) -- call superclass constructor
- attribute radius
- method print
expose radius say "A circle of radius" radius "centered at location ("||self~x","self~y")"
</lang> Output:
A point at location (3,2) A circle of radius 6 centered at location (0,2)
Method binding in ooRexx is late and dynamic. In many situations, polymorphism can be achieved merely by providing an expected method. It is not necessary for an object to be of a particular class hierarchy. In the example below, both point and circle implement a print method, but there is no class relationship between these classes other than what they inherit from the object class.
<lang ooRexx> p = .point~new(3,2) c = .circle~new(,2,6)
p~print c~print
- class point
- method init
expose x y use strict arg x = 0, y = 0 -- defaults to 0 for any non-specified coordinates
- attribute x
- attribute y
- method print
expose x y say "A point at location ("||x","y")"
- class circle
- method init
expose x y radius use strict arg x = 0, y = 0, radius = 0
- attribute radius
- attribute x
- attribute y
- method print
expose radius x y say "A circle of radius" radius "centered at location ("||x","y")"
</lang> Output:
A point at location (3,2) A circle of radius 6 centered at location (0,2)
OxygenBasic
Also uses method overloading, named parameters in the constructors, inheritance with method overrides.
Other primitives convert to floats automatically
A compact format for the methods is used to improve layout. <lang oxygenbasic> type tpoint float xx,yy type tcircle float xx,yy,rr
'========== class point '========== ' has tpoint ' method constructor (float x=0,y=0){this<=x,y} method destructor {} method V() as point {return @this} method V(tpoint*a) {this<=a.xx,a.yy} method V(point *a) {this<=a.xx,a.yy} method X() as float {return xx} method Y() as float {return yy} method X(float a) {xx=a} method Y(float a) {yy=a} method clear() {this<=.0,.0} method show() as string {return "x=" xx ", y=" yy } ' end class
'===========
class circle
'===========
'
has point
float rr
'
method constructor (float x=.0,y=.0,r=1.0){this<=x,y,r}
method V(tcircle*a) {this<=a.xx,a.yy,a.rr}
method V(circle *a) {this<=a.xx,a.yy,a.rr}
method R() as float {return rr}
method R(float a) {rr=a}
method clear() {this<=.0,.0,.0}
method show() as string {return "x=" xx ", y=" yy ", r=" rr }
'
end class
'===== 'TESTS '=====
new circle ca (r=.5) new circle cb (x=10,y=10) new circle cc (10,10,0.5)
cb.r="7.5" 'will convert a string value
cb.y=20
print cb.show 'result x=10, y=20 ,r=7.5
del ca : del cb : del cc </lang>
Oz
No inheritance necessary for polymorphism, so we don't use it here (a circle is certainly not a point). Default constructors are implemented by named default arguments. No accessors because we use immutable public attributes ("features").
<lang oz>class Point
feat x y meth init(x:X<=0.0 y:Y<=0.0) self.x = X self.y = Y end
meth print {System.showInfo "Point("# "x:"#self.x# ", y:"#self.y# ")"} end
end
class Circle
feat center r meth init(center:C<={New Point init} r:R<=1.0) self.center = C self.r = R end
meth print {System.showInfo "Circle("# "x:"#self.center.x# ", y:"#self.center.y# ", r:"#self.r# ")"} end
end</lang>
Pascal
See Delphi
Perl
What polymorphic function means in the context of Perl is as clear as mud. subs already can take anything as parameter by default. Destructors are automatic, so I dropped them. <lang perl>{
package Point; use Class::Spiffy -base; use Clone qw(clone); sub _print { my %self = %{shift()}; while (my ($k,$v) = each %self) { print "$k: $v\n"; } } sub members { no strict; grep { 1 == length and defined *$_{CODE} } keys %{*{__PACKAGE__."\::"}}; } sub new { my $class = shift; my %param = @_; $param{$_} = 0 for grep {!defined $param{$_}} members; bless \%param, $class; } sub copy_constructor { clone shift; } sub copy_assignment { my $self = shift; my $from = shift; $self->$_($from->$_) for $from->members; } field 'x'; field 'y';
}
{
package Circle; use base qw(Point); field 'r';
}
{
package main; $_->_print, print "\n" for ( Point->new, Point->new(x => 2), Point->new(y => 3), Point->new(x => 8, y => -5), ); my $p1 = Point->new(x => 8, y => -5); my $p2 = $p1->copy_constructor; print "we are really different objects, not just references ". "to the same instance\n" unless \$p1 eq \$p2; # accessors autogenerated $p1->x(1); $p1->y(2); print $p1->x, "\n"; print $p1->y, "\n"; $p2->copy_assignment($p1); print $p2->x, "\n"; print $p2->y, "\n"; print "we now have the same values, but we are still ". "different objects\n" unless \$p1 eq \$p2; $_->_print, print "\n" for ( Circle->new, Circle->new(x => 1), Circle->new(y => 2), Circle->new(r => 3), Circle->new(x => 4, y => 5), Circle->new(x => 6, r => 7), Circle->new(y => 8, r => 9), Circle->new(x => 1, y => 2, r => 3), ); my $c = Circle->new(r => 4); print $c->r, "\n"; # accessor autogenerated
}</lang>
Perl 6
All appropriate constructors, initializers, accessors, and destructors are provided by default, but may be explicitly declared for flexibility. To create only readonly accessors for better encapsulation, leave out all the "is rw" traits. Here we demonstrate that accessors can behave like variables and may be assigned. <lang perl6>class Point {
has Num $.x is rw = 0; has Num $.y is rw = 0; method Str { $.perl }
}
class Circle {
has Point $.p is rw = Point.new; has Num $.r is rw = 0; method Str { $.perl }
}
my $c = Circle.new(Point.new(x => 1, y => 2), r => 3); say $c; $c.p.x = (-10..10).pick; $c.p.y = (-10..10).pick; $c.r = (0..10).pick; say $c;</lang> In this case we define the Str coercion method polymorphically, which is used by say or print to format the contents of the object. We could also have defined print methods directly. We could have factored this method out to a common role and composed it into each class. We could also have defined multi subs outside of the class, like this: <lang perl6>multi print (Point $p) { $p.perl.print } multi print (Circle $c) { $c.perl.print }</lang>
PHP
'print' is a reserved keyword in PHP so the method to print is called 'output'. Alternatively the Point and Circle objects can be converted to a string representation by simply printing / echo'ing the object because the objects implement the magic '__toString' method.
Point class definition.
<lang PHP> class Point {
protected $_x;
protected $_y; public function __construct() { switch( func_num_args() ) { case 1: $point = func_get_arg( 0 ); $this->setFromPoint( $point ); break; case 2: $x = func_get_arg( 0 ); $y = func_get_arg( 1 ); $this->setX( $x ); $this->setY( $y ); break; default: throw new InvalidArgumentException( 'expecting one (Point) argument or two (numeric x and y) arguments' ); } } public function setFromPoint( Point $point ) { $this->setX( $point->getX() ); $this->setY( $point->getY() ); } public function getX() { return $this->_x; } public function setX( $x ) { if( !is_numeric( $x ) ) { throw new InvalidArgumentException( 'expecting numeric value' ); } $this->_x = (float) $x; } public function getY() { return $this->_y; } public function setY( $y ) { if( !is_numeric( $y ) ) { throw new InvalidArgumentException( 'expecting numeric value' ); } $this->_y = (float) $y; } public function output() { echo $this->__toString(); } public function __toString() { return 'Point [x:' . $this->_x . ',y:' . $this->_y . ']'; }
} </lang>
Circle class definition.
<lang PHP> class Circle extends Point {
private $_radius; public function __construct() { switch( func_num_args() ) { case 1: $circle = func_get_arg( 0 ); $this->setFromCircle( $circle ); break; case 2: $point = func_get_arg( 0 ); $radius = func_get_arg( 1 ); $this->setFromPoint( $point ); $this->setRadius( $radius ); break; case 3: $x = func_get_arg( 0 ); $y = func_get_arg( 1 ); $radius = func_get_arg( 2 ); $this->setX( $x ); $this->setY( $y ); $this->setRadius( $radius ); break; default: throw new InvalidArgumentException( 'expecting one (Circle) argument or two (Point and numeric radius) or three (numeric x, y and radius) arguments' ); } } public function setFromCircle( Circle $circle ) { $this->setX( $circle->getX() ); $this->setY( $circle->getY() ); $this->setRadius( $circle->getRadius() ); } public function getPoint() { return new Point( $this->getX(), $this->getY() ); } public function getRadius() { return $this->_radius; } public function setRadius( $radius ) { if( !is_numeric( $radius ) ) { throw new InvalidArgumentException( 'expecting numeric value' ); } $this->_radius = (float) $radius; } public function __toString() { return 'Circle [' . $this->getPoint() . ',radius:' . $this->_radius . ']'; }
} </lang>
Usage:
<lang PHP> $point = new Point( 1, 5 ); $circle = new Circle( 1, 5, 6 );
$point->output(); // or echo $point;
echo "\n";
$circle->output(); // or echo $circle; </lang>
Will result in:
Point [x:1,y:5]
Circle [Point [x:1,y:5],radius:6]
PicoLisp
<lang PicoLisp>(class +Point)
- x y
(dm T (X Y)
(=: x (or X 0)) (=: y (or Y 0)) )
(dm print> ()
(prinl "Point " (: x) "," (: y)) )
(class +Circle +Point)
- r
(dm T (X Y R)
(super X Y) (=: r (or R 0)) )
(dm print> ()
(prinl "Circle " (: x) "," (: y) "," (: r)) )</lang>
<lang PicoLisp>(setq
P (new '(+Point) 3 4) C (new '(+Circle) 10 10 5) )
(print> P) (print> C)</lang> Output:
Point 3,4 Circle 10,10,5
Pop11
When class is defined in Pop11 it automatically defines default constructors, slot accessors and copy operations. So it is enough to define classes and the print method.
<lang pop11>uses objectclass; define :class Point;
slot x = 0; slot y = 0;
enddefine;
define :class Circle;
slot x = 0; slot y = 0; slot r = 1;
enddefine;
define :method print(p : Point);
printf('Point(' >< x(p) >< ', ' >< y(p) >< ')\n');
enddefine;
define :method print(p : Circle);
printf('Circle(' >< x(p) >< ', ' >< y(p) >< ', ' >< r(p) >< ')\n');
enddefine;</lang>
To test we can use the following code:
<lang pop11>;;; Initialize variables using default constructors lvars instance1 = newPoint(); lvars instance2 = newCircle();
- Use print method
print(instance1); print(instance2);</lang>
PureBasic
Using the open-source precompiler SimlpeOOP. <lang PureBasic>Class MyPoint
BeginProtect x.i y.i EndProtect Public Method GetX() MethodReturn This\X EndMethod Public Method GetY() MethodReturn This\Y EndMethod Public Method SetX(n) This\X=n EndMethod Public Method SetY(n) This\Y=n EndMethod Public Method Print() PrintN("Point") EndMethod Public Method Init(x=0,y=0) This\x=x This\y=y EndMethod
EndClass
Class Circle Extends MyPoint
Protect Radie.i Public Method Circel(x=0, y=0, r=0) This\X = x This\y = y This\Radie=r EndMethod Public Method GetRadie() MethodReturn This\Radie EndMethod Public Method SetRadie(n) This\Radie = n EndMethod Public Method Print() PrintN("Circle: "+ _ " X= "+Str(This\X)+ _ " Y= "+Str(This\Y)+ _ " R= "+Str(This\Radie)) EndMethod
EndClass</lang> Testcode <lang PureBasic>*point.MyPoint = NewObject.MyPoint
- circle.Circle = NewObject.Circle
If OpenConsole()
*point\Print() *circle\SetX(3) *circle\Print() CloseConsole()
EndIf</lang>
Python
Multiple constructors are not needed because Python supports default values for arguments. Accessors are not needed because Python attributes are public. It is possible to add managed attributes later without changing the interface and existing client code. For the print function, use the standard __repr__ methods, used when printing an object. Destructors are not needed of course.
<lang python>class Point(object):
def __init__(self, x=0.0, y=0.0): self.x = x self.y = y def __repr__(self): return '<Point 0x%x x: %f y: %f>' % (id(self), self.x, self.y)
class Circle(object):
def __init__(self, center=None, radius=1.0): self.center = center or Point() self.radius = radius def __repr__(self): return '<Circle 0x%x x: %f y: %f radius: %f>' % ( id(self), self.center.x, self.center.y, self.radius)</lang>
Usage example:
>>> from polymorphism import Point, Circle >>> p1 = Point() >>> Point() <Point 0x5b1b0 x: 0.000000 y: 0.000000> >>> Point(3, 4) <Point 0x5b0f0 x: 3.000000 y: 4.000000> >>> Point(y=4) <Point 0x5b0b0 x: 0.000000 y: 4.000000> >>> Point(x=3) <Point 0x5b1b0 x: 3.000000 y: 0.000000> >>> Circle() <Circle 0x5b330 x: 0.000000 y: 0.000000 radius: 1.000000> >>> Circle(Point(3,4)) <Circle 0x5b3b0 x: 3.000000 y: 4.000000 radius: 1.000000> >>> Circle(Point(3,4), 7) <Circle 0x5b3d0 x: 3.000000 y: 4.000000 radius: 7.000000> >>> Circle(radius=10) <Circle 0x5b0f0 x: 0.000000 y: 0.000000 radius: 10.000000> >>> Circle(center=Point(127,0)) <Circle 0x5b0b0 x: 127.000000 y: 0.000000 radius: 1.000000> >>> p = Point(1.25, 3.87) >>> p <Point 0x5b3d0 x: 1.250000 y: 3.870000> >>> p.x = 10.81 >>> p <Point 0x5b3d0 x: 10.810000 y: 3.870000> >>> c = Circle(p, 21.4) >>> c <Circle 0x5b0b0 x: 10.810000 y: 3.870000 radius: 21.400000> >>> c.center.x = 1.0 >>> c <Circle 0x5b0b0 x: 1.000000 y: 3.870000 radius: 21.400000>
Or, using inheritance like some of the other solutions: <lang python>class Point(object):
def __init__(self, x=0.0, y=0.0): self.x = x self.y = y def __repr__(self): return '<Point 0x%x x: %f y: %f>' % (id(self), self.x, self.y)
class Circle(Point):
def __init__(self, x=0.0, y=0.0, radius=1.0): Point.__init__(self, x, y) self.radius = radius def __repr__(self): return '<Circle 0x%x x: %f y: %f radius: %f>' % ( id(self), self.x, self.y, self.radius)</lang>
Usage example:
>>> from polymorphism import Point, Circle >>> p1 = Point() >>> Point() <Point 0x5b1b0 x: 0.000000 y: 0.000000> >>> Point(3, 4) <Point 0x5b0f0 x: 3.000000 y: 4.000000> >>> Point(y=4) <Point 0x5b0b0 x: 0.000000 y: 4.000000> >>> Point(x=3) <Point 0x5b1b0 x: 3.000000 y: 0.000000> >>> Circle() <Circle 0x5b330 x: 0.000000 y: 0.000000 radius: 1.000000> >>> Circle(3, 4) <Circle 0x5b3b0 x: 3.000000 y: 4.000000 radius: 1.000000> >>> Circle(3, 4, 7) <Circle 0x5b3d0 x: 3.000000 y: 4.000000 radius: 7.000000> >>> Circle(radius=10) <Circle 0x5b0f0 x: 0.000000 y: 0.000000 radius: 10.000000> >>> Circle(x=127) <Circle 0x5b0b0 x: 127.000000 y: 0.000000 radius: 1.000000> >>> p = Point(1.25, 3.87) >>> p <Point 0x5b3d0 x: 1.250000 y: 3.870000> >>> p.x = 10.81 >>> p <Point 0x5b3d0 x: 10.810000 y: 3.870000> >>> c = Circle(p.x, p.y, 21.4) >>> c <Circle 0x5b0b0 x: 10.810000 y: 3.870000 radius: 21.400000> >>> c.x = 1.0 >>> c <Circle 0x5b0b0 x: 1.000000 y: 3.870000 radius: 21.400000>
Mutability
The task calls for the creation of mutable types i.e that you are allowed to change the values of x, y, or r of a Point or Circle after they have been created. If this is not needed, then the Python namedtuple is a good way to create immutable classes with named fields such as these. <lang python>>>> from collections import namedtuple >>> class Point(namedtuple('Point', 'x y')): def __new__( _cls, x=0, y=0 ): return super().__new__(_cls, x, y)
>>> class Circle(namedtuple('Circle', 'x y r')):
def __new__( _cls, x=0, y=0, r=0 ):
return super().__new__(_cls, x, y, r)
>>> Point(), Point(x=1), Point(y=2), Point(3, 4)
(Point(x=0, y=0), Point(x=1, y=0), Point(x=0, y=2), Point(x=3, y=4))
>>> Circle(), Circle(r=2), Circle(1, 2, 3)
(Circle(x=0, y=0, r=0), Circle(x=0, y=0, r=2), Circle(x=1, y=2, r=3))
>>> p = Point(1.25, 3.87)
>>> p
Point(x=1.25, y=3.87)
>>> p.x = 10.81
Traceback (most recent call last):
File "<pyshell#27>", line 1, in <module> p.x = 10.81
AttributeError: can't set attribute >>> </lang>
And if you don't need default arguments, this becomes: <lang python>>>> Point = namedtuple('Point', 'x y') >>> Circle = namedtuple('Circle', 'x y r') >>> Point(3, 4) Point(x=3, y=4) >>> Circle(x=1, y=2, r=3) Circle(x=1, y=2, r=3) >>> </lang>
R
Only the S4 class system is considered here. Copy constructors are not needed, since objects are copied by value. Neither are destructors needed (just use the rm function). <lang R>setClass("point",
representation( x="numeric", y="numeric"), prototype( x=0, y=0))
- Instantiate class with some arguments
p1 <- new("point", x=3)
- Access some values
p1@x # 3
- Define a print method
setMethod("print", signature("point"),
function(x, ...) { cat("This is a point, with location, (", x@x, ",", x@y, ").\n") })
print(p1)
- Define a circle class
setClass("circle",
representation( centre="point", r="numeric"), prototype( centre=new("point"), r=1))
circS4 <- new("circle", r=5.5)
- Access some values
circS4@r # 5.5 circS4@centre@x # 0
- Define a print method
setMethod("print", signature("circle"),
function(x, ...) { cat("This is a circle, with radius", x@r, "and centre (", x@centre@x, ",", x@centre@y, ").\n") })
print(circS4)</lang>
Ruby
We use attr_accessor to provide all the accessor and assignment operations. Default arguments eliminate the need for multiple constructors. The built-in puts uses the object's to_s method. Due to duck typing, the two classes do not need to inherit from each other. The Kernel#dup method can be used as a copy constructor.
<lang ruby>class Point
attr_accessor :x,:y def initialize(x=0,y=0) self.x=x self.y=y end def to_s "Point at #{x},#{y}" end
end
class Circle
attr_accessor :x,:y,:r def initialize(x=0,y=0,r=0) self.x=x self.y=y self.r=r end def to_s "Circle at #{x},#{y} with radius #{r}" end
end</lang> Example:
# create a point p = Point.new(1, 2) puts p # => Point at 1,2 puts p.x # => 1 # create a circle c = Circle.new(4,5,6) # copy it d = c.dup d.r = 7.5 puts c # => Circle at 4,5 with radius 6 puts d # => Circle at 4,5 with radius 7.5
Seed7
Seed7 object orientation works via interfaces. The example below introduces the interface type GraphicObj. To be usable an interface type needs also interface functions (which are defined with the keyword DYNAMIC). The interface function print is defined for GraphicObj. The struct types Point and Circle implement the the interface GraphicObj (they are implementation types). Note that Circle inherits x and y from Point. Functions which return a Point respectively Circle are used as constructors. Note that a Seed7 constructor does not need to have the name of the type (a new Point could be created with a function called abc). Seed7 defines copy constructor, assignment and destructor automatically.
<lang seed7>$ include "seed7_05.s7i";
const type: GraphicObj is new interface;
const proc: print (in GraphicObj: aGraphicObj) is DYNAMIC;
const type: Point is new struct
var integer: x is 0; var integer: y is 0; end struct;
type_implements_interface(Point, GraphicObj);
const func Point: Point (in integer: x, in integer: y) is func
result var Point: newPoint is Point.value; begin newPoint.x := x; newPoint.y := y; end func;
const proc: print (in Point: aPoint) is func
begin writeln("Point(" <& aPoint.x <& ", " <& aPoint.y <& ")"); end func;
const type: Circle is sub Point struct
var integer: r is 0; end struct;
type_implements_interface(Circle, GraphicObj);
const func Circle: Circle (in integer: x, in integer: y, in integer: r) is func
result var Circle: newCircle is Circle.value; begin newCircle.x := x; newCircle.y := y; newCircle.r := r; end func;
const proc: print (in Circle: aCircle) is func
begin writeln("Circle(" <& aCircle.x <& ", " <& aCircle.y <& ", " <& aCircle.r <& ")"); end func;
const proc: main is func
local var Point: pnt is Point(1, 2); var Circle: circ is Circle(3, 4, 5); var GraphicObj: graph is Point.value; begin graph := pnt; print(graph); graph := circ; print(graph); end func;</lang>
- Output:
Point(1, 2) Circle(3, 4, 5)
SIMPOL
In SIMPOL any type can be declared to be tagged with a name. That name can then be used to define a variable that can hold a reference to any type tagged with the same name. Multiple constructors are not needed, since all the parameters can be provided in the same constructor call. Types embedded in other types resolve according to the rules in SIMPOL such that if a property name is used that is not present in the actual type definition, then a depth first search starting at the beginning of the type definition will resolve a matching property or method name of an embedded type. This resolution is not performed on properties defined as reference
are not used in the extended dot operator resolution mechanism unless they are also assigned the resolve
keyword. The embed
keyword in the type definition states that the type itself can be embedded in another type (any type can be placed as a reference in another type).
<lang simpol>type mypoint(mypoint) embed export
embed integer x integer y
reference function copy function print
end type
function mypoint.new(mypoint me, integer x=0, integer y=0)
me.x = x me.y = y
end function me
function mypoint.copy(mypoint me)
mypoint p
p =@ mypoint.new(me.x, me.y)
end function p
function mypoint.print(mypoint me)
end function "mypoint"
type circle(mypoint) embed export
reference mypoint midpoint resolve
embed integer radius
reference function copy function print
end type
function circle.new(circle me, integer x=0, integer y=0, integer radius=0, mypoint midpoint)
if midpoint =@= .nul me.midpoint =@ mypoint.new(x, y) else me.x = midpoint.x me.y = midpoint.y end if
me.radius = radius
end function me
function circle.copy(circle me)
circle c
c =@ circle.new(radius=me.radius, midpoint=me.midpoint)
end function c
function circle.print(circle me)
end function "circle"
function main()
type(mypoint) p, c string result
p =@ mypoint.new() c =@ circle.new()
result = p.print() + "{d}{a}" + c.print() + "{d}{a}"
end function result</lang>
SIMPOL does not currently have access to stdin, stdout, and stderr, so to return a value from the program to a console, it must be as part of the return value.
Smalltalk
Like Python and Ruby, these objects do not need to be related in order to have polymorphic methods. <lang smalltalk>!Object subclass: #Point
instanceVariableNames: 'x y' classVariableNames: poolDictionaries: category: 'polymorphism' !
!Point class methodsFor: 'instance creation'! new
^self newBasic x := 0; y := 0 ! !
!Point class methodsFor: 'instance creation'! x: x y: y
^self newBasic x := x; y := y ! !
!Point methodsFor: 'member access'! x
^x ! !
!Point methodsFor: 'member access'! y
^y ! !
!Point methodsFor: 'member access'! x: x
^self x := x ! !
!Point methodsFor: 'member access'! y: y
^self y := y ! !
!Point methodsFor: 'member access'! x: x y: y
^self x := x; y := y ! !
!Point methodsFor: 'polymorphism test'! print
Transcript show: x; space; show: y ! !
!Object subclass: #Circle
instanceVariableNames: 'center r' classVariableNames: poolDictionaries: category: 'polymorphism' !
!Circle class methodsFor: 'instance creation'! new
^self newBasic center := Point new; r := 0 ! !
!Circle class methodsFor: 'instance creation'! radius: radius
^self newBasic center := Point new; r := radius ! !
!Circle class methodsFor: 'instance creation'! at: point radius: r
^self newBasic center := point; r := r ! !
!Circle methodsFor: 'member access'! center
^center ! !
!Circle methodsFor: 'member access'! x: x y: y
^self center x: x y: y ! !
!Circle methodsFor: 'member access'! radius
^r ! !
!Circle methodsFor: 'member access'! radius: radius
^self r := radius ! !
!Circle methodsFor: 'polymorphism test'! print
Transcript show: center; space; show: radius ! !</lang>
TODO: more idiomatic mechanism for presenting objects as strings. TODO: fill in more methods
Tcl
or
Since Tcl's objects have their methods invoked by sending a (potentially-interceptable) message to them, allowing them to even respond to method calls that are not explicitly declared on them, there is no need for the objects to be formally related. We only do so here for convenience. In addition, Tcl's arguments to commands, procedures and methods are all fully polymorphic by default. <lang tcl>package require TclOO oo::class create Point {
variable X Y constructor {x y} { set X $x set Y $y } method x args { set X {*}$args } method y args { set Y {*}$args } method print {} { puts "Point($X,$Y)" } method copy {} { set copy [oo::copy [self]] $copy x $X $copy y $Y return $copy }
} oo::class create Circle {
superclass Point variable R constructor {x y radius} { next $x $y set R $radius } method radius args { set R {*}$args } method print {} { puts "Circle([my x],[my y],$R)" } method copy {} { set copy [next] $copy radius $R return $copy }
}
- No destructors: unneeded by these classes
set p [Point new 1.0 2.0] set c [Circle new 3.0 4.0 5.0] set cCopy [$c copy] puts "$p is at ([$p x],[$p y])" $c radius 1.5 set objects [list $p $c $cCopy] foreach o $objects {
$o print
}</lang>
- Programming Tasks
- Basic language learning
- Object oriented
- ActionScript
- Ada
- Aikido
- BASIC
- BBC BASIC
- C
- C++
- C sharp
- Clojure
- Common Lisp
- D
- Delphi
- E
- Eiffel
- Ela
- Factor
- Forth
- Fortran
- F Sharp
- Go
- Haskell
- Unicon
- Inform 7
- J
- Java
- JavaScript
- Lua
- NetRexx
- Objeck
- Objective-C
- OCaml
- OoRexx
- OxygenBasic
- Oz
- Pascal
- Perl
- Perl 6
- PHP
- PicoLisp
- Pop11
- PureBasic
- Python
- R
- Ruby
- Seed7
- SIMPOL
- Smalltalk
- Tcl
- TclOO
- ALGOL 68/Omit
- GUISS/Omit
- Mathematica/Omit
- Maxima/Omit
- ML/I/Omit
- PARI/GP/Omit
- TI-83 BASIC/Omit
- TI-89 BASIC/Omit