How to subclass in Go - oop

Question

In C I can do something like this
struct Point {
int x,y;
}
struct Circle {
struct Point p; // must be first!
int rad;
}
void move(struct Point *p,int dx,int dy) {
....
}
struct Circle c = .....;
move( (struct Point*)&c,1,2);
Using this approach, I can pass any struct(Circle,Rectangle,etc) that has struct Point as first member.
How can I do the same in google go?

Answer 1

Actually, there's a simpler way to do it, which is more similar to the OP's example:
type Point struct {
x, y int
}
func (p *Point) Move(dx, dy int) {
p.x += dx
p.y += dy
}
type Circle struct {
*Point // embedding Point in Circle
rad int
}
// Circle now implicitly has the "Move" method
c := &Circle{&Point{0, 0}, 5}
c.Move(7, 3)
Also notice that Circle would also fulfill the Mover interface that PeterSO posted.
http://golang.org/doc/effective_go.html#embedding

Answer 2

Although Go has types and methods and
allows an object-oriented style of
programming, there is no type
hierarchy. The concept of “interface”
in Go provides a different approach
that we believe is easy to use and in
some ways more general. There are also
ways to embed types in other types to
provide something analogous—but not
identical—to subclassing. Is Go an
object-oriented language?, FAQ.
For example,
package main
import "fmt"
type Mover interface {
Move(x, y int)
}
type Point struct {
x, y int
}
type Circle struct {
point Point
rad int
}
func (c *Circle) Move(x, y int) {
c.point.x = x
c.point.y = y
}
type Square struct {
diagonal int
point Point
}
func (s *Square) Move(x, y int) {
s.point.x = x
s.point.y = y
}
func main() {
var m Mover
m = &Circle{point: Point{1, 2}}
m.Move(3, 4)
fmt.Println(m)
m = &Square{3, Point{1, 2}}
m.Move(4, 5)
fmt.Println(m)
}