pointer_receiver.go

package main

import (
	"fmt"
	"math"
)

func main() {
	var i interface{}
	describe(i)
	
	i = 42
	describe(i)
	
	i = "hello"
	describe(i)
	
	//
	v := &Vertex{3, 4}
	fmt.Println(v.Abs())
}

type MyFloat float64

func (f MyFloat) Abs() float64 {
	if f < 0 {
		// neg
		return float64(-f)
	}
	return float64(f)
}

type Vertex struct {
	X, Y float64
}

// method
func (v Vertex) Abs() float64 {
	return math.Sqrt(v.X*v.X + v.Y*v.Y)
}

// methods are function
func Abs(v Vertex) float64 {
	return math.Sqrt(v.X*v.X + v.Y*v.Y)
}

// pointer receiver
// This means the receiver type has the literal syntax *T for some type T.
// Also, T cannot itself be a pointer such as *int
func (v *Vertex) Scale(f float64) {
	v.X = v.X * f
	v.Y = v.Y * f
}

func describe(i interface{}) {
	fmt.Printf("(%v, %T)\n", i, i)
}

https://tour.golang.org/methods/4