Golang interaces example, from: https://youtu.be/EGRXKV6j-v0

interfaces.go

package main

import (
  "fmt"
  "math"
)

type rectangle struct {
  width float64
  height float64
}

type circle struct {
  radius float64
}

type triangle struct {
  height float64
  width float64
  b float64
  c float64
}

func (r rectangle) area() float64 {
  return r.height * r.width
}

func (c circle) area() float64 {
  return math.Pi * math.Exp(c.radius)
}

func (t triangle) area() float64 {
  return (t.height * t.width) / 2
}

func (r rectangle) perim() float64 {
  return (2 * r.height) + (2 * r.width)
}

func (c circle) perim() float64 {
  return 2 * math.Pi * c.radius
}

func (t triangle) perim() float64 {
  return t.width + t.b + t.c
}

type geometry interface {
  area() float64
  perim() float64
}

func calc (g geometry) {
  fmt.Println("Area: ", g.area())
  fmt.Println("Perim:",g.perim())
}

func main() {
  rect := rectangle {height: 2, width: 5}
  circle := circle {radius: 2}
  tri := triangle {height: 2, width: 3, b: 3, c: 1}

  for _, shape := range [3]geometry{rect, circle, tri} {
    calc(shape)
  }
}