Tour of Go 2.0

Nil interface values

A nil interface value holds nothing — no concrete value, no concrete type.

Calling a method on it causes a runtime panic. There’s no type information to dispatch on, so Go has nowhere to go.

Try it: run this code and see the panic. This is different from the previous example — here i has no type at all, not even a nil-valued one.

main.go ▶ Run in Playground 
package main

import "fmt"

type I interface {
	M()
}

func main() {
	var i I
	describe(i)
	i.M()
}

func describe(i I) {
	fmt.Printf("(%v, %T)\n", i, i)
}