Polymorphism
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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
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.
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;
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;
The following is the child package defining the Circle type.
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;
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;
The following procedure is an entry point for a program, serving the same purpose as the main function in C.
with Shapes.Circles; use Shapes.Circles; use Shapes; procedure Shapes_Main is P : Point; C : Circle; begin Print(P); Print(C); end Shapes_Main;
BASIC
C
Compiler: GCC, MSVC, BCC, Watcom
Libraries: Standard
/* After reading this you may understand */ /* why Bjarne Stroustrup's invented C++ */ #if defined( _WIN32 ) || defined( MSC_VER ) #define FN_PTR(x) (& x) #else #define FN_PTR(x) (x) #endif
typedef struct Point { int x; int y; void (*dtor)(); /* virtual */ void (*print)(); /* virtual */ } Point;
Point* Point_new0() { Point* pthis = (Point*) malloc( sizeof( Point ) ); memset(pthis, 0, sizeof( Point ) ); pthis->dtor = FN_PTR(Point_dtor); pthis->print = FN_PTR(Point_print); }
Point* Point_new1(int x0) { Point* pthis = (Point*) malloc( sizeof( Point ) ); pthis->x = x0; pthis->y = 0; pthis->dtor = FN_PTR(Point_dtor); pthis->print = FN_PTR(Point_print); }
Point* Point_new2(int x0, int y0) { Point* pthis = (Point*) malloc( sizeof( Point ) ); pthis->x = x0; pthis->y = y0; pthis->dtor = FN_PTR(Point_dtor); pthis->print = FN_PTR(Point_print); }
void Point_delete(Point** pthis) { if(pthis && *pthis) { (*pthis)->dtor(); free(*pthis); *pthis = NULL; } }
Point* Point_copy(Point* p) { Point* pthis = (Point*) malloc( sizeof( Point ) ); memcpy(pthis, p, sizeof( Point ) ); pthis->dtor = FN_PTR(Point_dtor); pthis->print = FN_PTR(Point_print); return pthis; }
int Point_getX(Point* pthis) { return pthis->x; } int Point_getY(Point* pthis) { return pthis->y; } int Point_setX(Point* pthis, int x0) { pthis->x = x0; } int Point_setY(Point* pthis, int y0) { pthis->y = y0; } void Point_print() { printf("Point\n"); } void Point_dtor() {}
// Trick: This way Circle.x, Circle.y, Circle.r are available typedef union Circle { Point point; struct _Circle { Point point; int r; }; } Circle;
Circle* Circle_new0() { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); memset(pthis, 0, sizeof( Circle ) ); pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
Circle* Circle_new1(int x0) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); pthis->x = x0; pthis->y = 0; pthis->r = 0; pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
Circle* Circle_new2(int x0, int y0) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); pthis->x = x0; pthis->y = y0; pthis->r = 0; pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
Circle* Circle_new3(int x0, int y0, int r0) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); pthis->x = x0; pthis->y = y0; pthis->r = r0; pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
Circle* Circle_newP0(Point* p) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); pthis->x = p->x; pthis->y = p->y; pthis->r = 0; pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
Circle* Circle_newP1(Point* p, int r0) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); pthis->x = p->x; pthis->y = p->y; pthis->r = r0; pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); }
void Circle_delete(Circle** pthis) { if(pthis && *pthis) { (*pthis)->dtor(); free(*pthis); *pthis = NULL; } }
Circle* Circle_copy(Circle* c) { Circle* pthis = (Circle*) malloc( sizeof( Circle ) ); memcpy(pthis, c, sizeof( Circle ) ); pthis->dtor = FN_PTR(Circle_dtor); pthis->print = FN_PTR(Circle_print); return pthis; }
int Circle_getX(Circle* pthis) { return pthis->x; } int Circle_getY(Circle* pthis) { return pthis->y; } int Circle_getR(Circle* pthis) { return pthis->r; } int Circle_setX(Circle* pthis, int x0) { pthis->x = x0; } int Circle_setY(Circle* pthis, int y0) { pthis->y = y0; } int Circle_setR(Circle* pthis, int r0) { pthis->r = r0; } void Circle_print() { printf("Circle\n"); } void Circle_dtor() {}
int main() { Point* p = Point_new0(); Point* c = (Point*)Circle_new0(); p->print(); c->print(); return 0; }
C++
Compiler: GCC, Visual C++, BCC, Watcom
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; }
Pattern: Curiously Recurring Template Pattern
Compiler: GCC, Visual C++, BCC, Watcom
// 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; }
C#
using System; 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 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.Console.WriteLine("Point"); } }
public class Circle : Point { private int r; public Circle(Point p) : this(p,0) { } public Circle(Point p, int r0) : base(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) : base(x0,y0) { r = r0; } public int getR() { return r; } public int setR(int r0) { r = r0; } 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(); } }
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 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 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(); } }