methods for struct _ golang

package main

import (
    "fmt"
)

type rect struct {
    width, height int
}

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

func (r rect) perim() int {
    return 2*r.width + 2*r.height
}

func main() {

    r := rect{width: 10, height: 5}

    fmt.Println("area : ", r.area())
    fmt.Println("perim : ", r.perim())

    rp := &r
    fmt.Println("area : ", rp.area())
    fmt.Println("perim : ", rp.perim())
}

area :  50
perim :  30
area :  50
perim :  30