Functions Overloading in interface and classes - how to? - class

Question

I have this interface :
interface IPoint {
getDist(): string;
getDist(x: number): any;
}
and I need a class to implement it but I can't get the right syntax to implement the getDist() method
in the class..
class Point implements IPoint {
// Constructor
constructor (public x: number, public y: number) { }
pointMethod() { }
getDist() {
Math.sqrt(this.x * this.x + this.y * this.y);
}
// Static member
static origin = new Point(0, 0);
}
it says:
Class 'Point' declares interface 'IPoint' but does not implement it:
Types of property 'getDist' of types 'Point' and 'IPoint' are
incompatible:Call signatures of types '() => void' and '{ (): string;
(x: number): any; }' are incompatible
What's the proper way to do this?
Thanks

Answer 1

When you declare the function in the class you need to decorate it with the overloads:
getDist(): string;
getDist(x: number): any;
getDist(x?: number): any {
// your code
}

Answer 2

This answer describes how to implement method overloading in TypeScript, and it's not pretty:
interface IPoint {
getDist(): string;
getDist(x: number): any;
}
class Point implements IPoint {
// Constructor
constructor (public x: number, public y: number) { }
pointMethod() { }
getDist(x?: number) {
if (x && typeof x == "number") {
return 'foo';
} else {
return 'bar';
}
}
}
N.B. with the particular combination of declared return types in the interface, you are limited to returning strings from getDist.

Answer 3

also you can use the default value
interface Foo{
next()
next(steps: number)
prev()
prev(steps: number)
}
next(steps: number = 1) {
// ...
}
prev(steps: number = 1) {
// ...
}

Answer 4

The following is a variation on some of the above
class Position {
x: number;
y: number;
constructor(x : number = 0, y : number = 0) {
this.x = x;
this.y = y;
}
}
class Pen {
colour: string;
constructor(colour: string) {
this.colour = colour;
}
}
class PlottingHead {
isPenUp: boolean;
pen: Pen;
position: Position;
constructor() {
this.penUp();
}
move(p: Position): void;
move(x: number, y: number): void;
move(x: number | Position, y?: number): void {
if (typeof x === "number")
{
x = new Position(x, y);
}
this.penUp();
this.position = x;
}
draw(x: number | Position, y?: number): void {
if (typeof x === "number")
{
x = new Position(x, y);
}
this.penDown();
this.position = x;
}
penDown(): void {
this.isPenUp = false;
}
penUp(): void {
this.isPenUp = true;
}
onChangePen(newPen: Pen) {
this.penUp();
this.pen = newPen;
}
}
The move function takes either a single position object or a pair of numeric values. This can obviously be extended as required.