inheritance and polymorphism together in golang, are possible? - go

Question

This question comes form the porting I have to do from a working logic of C++ program, to a golang context.
This is just an example, and i see how wierd it can be, but think about the logic behind it.
If the explanation bores you, go to the code, it is pretty self explanatory.. otherwise I try to explain.
The concept is that I have a base class that contains a method with common logic, but that methot use virtual function that each descendant need to implement.
In go, I easly achieve inheritance of the base method, but the polimorphic adaptation to the descendant it's complicate (for me): I can't figure out how replicate this mechanism..
class TPolygon{
private:
int nside;
public:
TPolygon(int n){ nside=n; }
virtual float Area()=0;
float MeanArea(){ return Area()/nside; }
};
class TSquare: public TPolygon{
private:
float side;
public:
TSquare(float sidelen):TPolygon(4){ side=sidelen; }
float Area(){ return side*side; }
};
class TTriangle: public TPolygon{
private:
float base, height;
public:
TTriangle(float b, float h):TPolygon(3){ base=b; height=h; }
float Area(){ return base*height/2; }
};
TSquare *square=new TSquare(2.0);
square->MeanArea(); // -> 2*2 / 4 correct
TTriangle *triangle=new TTriangle(5.0, 6.0);
triangle->MeanArea(); // -> 5*6/2 / 3 correct
in go i tried:
type TPolygon struct {
nside int
}
func (p *TPolygon) Area() float64 {
return 0
}
func (p *TPolygon) MeanArea() float64 {
return p.Area() / float64(p.nside)
}
type TSquare struct {
TPolygon
side float64
}
func NewSquare(sidelength float64) *TSquare {
return &TSquare{
TPolygon: TPolygon{nside: 4},
side: sidelength,
}
}
func (s *TSquare) Area() float64 {
return s.side * s.side
}
type TTriangle struct {
TPolygon
base, height float64
}
func NewTriangle(b, h float64) *TTriangle {
return &TTriangle{
TPolygon: TPolygon{nside: 3},
base: b,
height: h,
}
}
func (t *TTriangle) Area() float64 {
return t.base * t.height / 2
}
square := NewSquare(2.0)
square.MeanArea() // -> 0 from TPolygon.Area()
The only way I found to achieve this, is a workaround that break the DRY principle because need to repeat the same method in each descendant
func (p *TPolygon) meanArea2(a float64) float64 {
return a / float64(p.nside)
}
func (s *TSquare) MeanArea2() float64 {
return s.meanArea2(s.Area())
}
func (t *TTriangle) MeanArea2() float64 {
return t.meanArea2(t.Area())
}
square.MeanArea2() // -> 1 as expected
and moreover, isn't always easy and possible to refactor this way, if the logic get more complicate..
Does anybody knows if this architecture is possible in golang, and how?
Or if there is other workaround that get close?

Answer 1

There are ways to emulate inheritance, but the following is much cleaner. It allows calculating the area/nsides value for any type that implements the two methods:
type MeanAreaSupport interface {
NSides() int
Area() float64
}
func MeanArea(shape MeanAreaSupport) float64 {
return shape.Area()/shape.NSides()
}