package main

import (
    "fmt"
)

type vertex struct {
    x, y float64
}

// note that this one can deal fine with a copy:
func (v vertex) abs() float64 {
    return v.x + v.y
}

// but this function needs access to the actual struct members
func (v *vertex) scale(s float64) {
    v.x *= s
    v.y *= s
}

type myfloat float64

func (f myfloat) abs() float64 {
    if f < 0 {
        return float64(-f)
    }
    return float64(f)
}

func main() {
    v := vertex{1.1, 2.2}
    fmt.Println(v.abs())
    v.scale(12)
    fmt.Println(v.abs())

    f := myfloat(12.23)
    fmt.Println(f.abs())
    fmt.Println(-f)
    fmt.Println((-f).abs())
}