How to use interfaces in golang from https://www.youtube.com/watch?v=lh_Uv2imp14

21-struct-methods.go

package main

import "fmt"

type Box struct {
	name   string
	colors []int
	age    int
}

func (b Box) getAge() int {
	return b.age
}

func (b *Box) setAge(age int) {
	b.age = age
}

func (b Box) getAvColors() float32 {
	sum := 0
	for _, v := range b.colors {
		sum += v
	}
	return float32(sum) / float32(len(b.colors))
}

func (b Box) getMaxColour() int {
	curMax := 0
	for _, v := range b.colors {
		if curMax < v {
			curMax = v
		}
	}
	return curMax
}

func main() {
	b1 := Box{"my box", []int{6, 7, 50}, 6}
	b2 := Box{"my box", []int{78, 7, 50}, 6}
	fmt.Println(b1.getAge())
	b1.setAge(9)
	fmt.Println(b1.getAge())
	fmt.Println(b1.getAvColors())
	fmt.Println(b2.getAvColors())
	fmt.Println(b2.getMaxColour())
}

22-interfaces.go

package main

import (
	"fmt"
	"math"
)

type shape interface {
	area() float64
}

type circle struct {
	radius float64
}

type rect struct {
	width  float64
	height float64
}

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

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

func getArea(s shape) float64 {
	return s.area()
}

func main() {
	c1 := circle{4.5}
	r1 := rect{5, 7}
	shapes := []shape{c1, &r1}

	for _, shape := range shapes {
		fmt.Println(getArea(shape))
	}
}