Interfaces

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// Create Interface
interface Shape = {
	func area = (this) -> F32;
	func num_sides = () -> UInt { return 0;	} // method with default
}


type Quad = struct {
	var width: F32;
	var height: F32;


	func area = (this) -> F32 {
		return this.width * this.height;
	}

	func num_sides = () -> UInt { return 4; }


	// implementation of Shape for Quad
	impl Shape{
		num_sides = num_sides,
		area      = area,
	}
}


type Circle = struct {
	var radius: F32;


	func get_area = (this) -> F32 {
		return 3.14 * this.radius * this.radius;
	}

	func get_num_sides = () -> UInt { return 0; }


	// Implementation of Shape for Circle
	impl Shape{
		num_sides = get_num_sides, // method names don't have to be the same
		// using default for Shape.area
	}
}



// this function becomes a template on the shape passed to it
func get_shape_num_sides = (shape: Shape) -> UInt {
	return shape.num_sides();
}


// runtime polymorphism
// `shape` is a struct of a pointer to the specific shape and a pointer to a `vtable`
func get_shape_area = (shape: Shape*) -> UInt {
	return shape.area();
}



func entry = () #entry -> UI8 {
	const quad = new Quad{
		width  = 1.0,
		height = 2.0,
	};

	const circle = new Circle{
		radius = 2.0,
	};

	const num_sides_of_quad: UInt = get_shape_num_sides(quad);

	const area_of_circle: F32 = get_shape_area(&circle as Shape*);
	
	return 0;
}