Tour of Go 2.0

Methods and pointer indirection

Here’s something useful: pointer receiver methods are more flexible than pointer-argument functions.

A plain function with a pointer argument requires a pointer — no exceptions:

var v Vertex
ScaleFunc(v, 5)  // Compile error!
ScaleFunc(&v, 5) // OK

But a method with a pointer receiver accepts both a value and a pointer:

var v Vertex
v.Scale(5)  // OK
p := &v
p.Scale(10) // OK

Go handles the conversion automatically. v.Scale(5) becomes (&v).Scale(5) behind the scenes. It’s a convenience — you don’t have to think about it.

main.go ▶ Run in Playground 
package main

import "fmt"

type Vertex struct {
	X, Y float64
}

func (v *Vertex) Scale(f float64) {
	v.X = v.X * f
	v.Y = v.Y * f
}

func ScaleFunc(v *Vertex, f float64) {
	v.X = v.X * f
	v.Y = v.Y * f
}

func main() {
	v := Vertex{3, 4}
	v.Scale(2)
	ScaleFunc(&v, 10)

	p := &Vertex{4, 3}
	p.Scale(3)
	ScaleFunc(p, 8)

	fmt.Println(v, p)
}