On 5/16/22 17:10, Alain De Vos wrote:
Let's say a shape is ,a circle with a radius ,or a square with a
rectangular size.
I want to pass shapes to functions, eg to draw them on the screen,
draw(myshape) or myshape.draw();
But how do i implement best shapes ?
There are many ways of achieving this but I think you are looking for
the classic object-oriented (OOP) shape hierarchy. (Option 2 below.)
1) This option does not use OOP. It uses function overloading:
import std.stdio;
struct Circle {
float radius;
}
void draw(Circle circle) {
writeln("This circle's radius is ", circle.radius);
}
struct Rectangle {
float width;
float height;
}
void draw(Rectangle rectangle) {
writefln!"This rectangle's dimensions are %sx%s."(rectangle.width,
rectangle.height);
}
void main() {
draw(Circle(1.5));
draw(Rectangle(2.5, 3.5));
}
That's very simple but it does not allow putting different types of
shapes e.g. in the same array.
2) If you want to have a shape hierarchy, then you can start by defining
its interface and implement that interface by concrete shape types.
Drawing is ordinarily handled by member functions:
import std.stdio;
// This defines what we can do with a Shape:
interface Shape {
void draw();
}
// This type is now a 'class' that implements Shape.
class Circle : Shape {
float radius;
// Classes require constructors; so here is one:
this (float radius) {
this.radius = radius;
}
// No parameter needed. This function always executes on
// 'this' object.
void draw() {
writeln("This circle's radius is ", radius);
}
}
// Similarly, a class
class Rectangle : Shape {
float width;
float height;
this(float width, float height) {
this.width = width;
this.height = height;
}
void draw() {
writefln!"This rectangle's dimensions are %sx%s."(width, height);
}
}
// Here is the promise of polymorphism: This function takes
// a Shape but the special drawing of each shape type is
// handled automatically.
void use(Shape shape) {
shape.draw();
}
void main() {
// Class hierarchies allow putting different types into
// the same array:
Shape[] shapes;
// Let's populate with alternating circles and rectangles
foreach (i; 1 .. 10) {
if (i % 2) {
shapes ~= new Circle(i);
} else {
shapes ~= new Rectangle(i, i * 2);
}
}
// And finally let's use them
foreach (shape; shapes) {
use(shape);
}
}
Ali
