Gekapselter Abstrakter Datentyp mittels Opaker Handles und Funktionstabellen-Strukturen

struct ShapeVTable;
 
typedef struct Shape {
    const struct ShapeVTable *vtable;
} Shape;
 
struct ShapeVTable {
    double (*area)(const Shape *self);
    void (*destroy)(Shape *self);
};
 
typedef struct {
    Shape base;
    double radius;
} Circle;
 
static double circle_area(const Shape *self) {
    const Circle *c = (const Circle *)self;
    return 3.1415926535 * c->radius * c->radius;
}
 
static const struct ShapeVTable circle_vtable = { .area = circle_area, .destroy = NULL };
 
void circle_init(Circle *c, double r) {
    c->base.vtable = &circle_vtable;
    c->radius = r;
}