Tour of Go 2.0

Methods continued

Methods aren’t limited to structs. You can define them on any type — as long as it’s defined in the same package.

Here, MyFloat is a numeric type with its own Abs method. No struct needed.

One rule: you can’t define a method on a type from another package. That means no adding methods to int, string, or any other built-in type directly.

Try it: change MyFloat to a negative value and watch Abs handle it.

main.go ▶ Run in Playground 
package main

import (
	"fmt"
	"math"
)

type MyFloat float64

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

func main() {
	f := MyFloat(-math.Sqrt2)
	fmt.Println(f.Abs())
}