SOLID: prinsip open/closed di golang

open_close.go

package main

import (
	"fmt"
	"math"
)

type tanah interface {
	luas(size float32) float32
}

type lingkaran struct{}

func (l *lingkaran) luas(diameter float32) float32 {
	jari2 := diameter / 2
	return math.Phi * jari2 * jari2
}

type persegi struct{}

func (p *persegi) luas(panjang float32) float32 {
	return panjang * panjang
}

type calculator struct {
	t tanah
}

func (c calculator) luas(ukuran float32) float32 {
	return c.t.luas(ukuran)
}

func main() {
	// open for extension, but closed for modification.
	bunder := calculator{t: &lingkaran{}}
	persegi := calculator{t: &persegi{}}

	fmt.Println(bunder.luas(3))  // 4
	fmt.Println(persegi.luas(3)) // 2
}