Tour of Go 2.0

Methods and pointer indirection (2)

The same flexibility works in reverse for value receivers.

A function taking a value argument requires exactly a value — pass a pointer and it won’t compile:

var v Vertex
fmt.Println(AbsFunc(v))  // OK
fmt.Println(AbsFunc(&v)) // Compile error!

But a method with a value receiver accepts both:

var v Vertex
fmt.Println(v.Abs()) // OK
p := &v
fmt.Println(p.Abs()) // OK

When you call p.Abs() on a pointer, Go automatically dereferences it: (*p).Abs(). Clean and consistent.

main.go ▶ Run in Playground 
package main

import (
	"fmt"
	"math"
)

type Vertex struct {
	X, Y float64
}

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

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

func main() {
	v := Vertex{3, 4}
	fmt.Println(v.Abs())
	fmt.Println(AbsFunc(v))

	p := &Vertex{4, 3}
	fmt.Println(p.Abs())
	fmt.Println(AbsFunc(*p))
}