Golang "inheritance" by composition and polymorphic classes

poly.go

package main

import (
	"fmt"
	"math"
)

type (
	Shape interface {
		GetCoords() (float64, float64)
		GetType() string
		GetArea() float64
	}
)

type shapeBase struct {
	X float64
	Y float64
}

func (s *shapeBase) GetCoords() (float64, float64) {
	return s.X, s.Y
}

type Circle struct {
	shapeBase
	Radius float64
}

func NewCircle(x, y, radius float64) *Circle {
	return &Circle{shapeBase: shapeBase{X: x, Y: y}, Radius: radius}
}

func (c *Circle) GetType() string {
	return "circle"
}

func (c *Circle) GetArea() float64 {
	return 2 * math.Pi * c.Radius
}

type Rectangle struct {
	shapeBase
	Width  float64
	Height float64
}

func NewRectangle(x, y, w, h float64) *Rectangle {
	return &Rectangle{shapeBase: shapeBase{X: x, Y: y}, Width: w, Height: h}
}

func (r *Rectangle) GetType() string {
	return "rectangle"
}

func (r *Rectangle) GetArea() float64 {
	return r.Width * r.Height
}

func PrintShapes(shapes []Shape) {
	for _, s := range shapes {
		x, y := s.GetCoords()
		fmt.Printf("position: (%.2f, %.2f), type: %s, area: %.2f\n",
			x, y,
			s.GetType(),
			s.GetArea())
	}
}

func main() {
	shapes := []Shape{
		NewCircle(100, 100, 3),
		NewRectangle(50, 50, 10, 60),
	}

	PrintShapes(shapes)
}

run.sh

roy@desktop:~/Projects/scratch/poly$ go build poly.go 
roy@desktop:~/Projects/scratch/poly$ ./poly 
position: (100.00, 100.00), type: circle, area: 18.85
position: (50.00, 50.00), type: rectangle, area: 600.00