Tour of Go 2.0

The empty interface

An interface with zero methods is the empty interface:

interface{}

Every type satisfies it — since every type implements at least zero methods. That means interface{} can hold any value of any type.

You’ll see it wherever code needs to handle unknown types: fmt.Print, JSON decoding, generic containers. It’s Go’s escape hatch from the type system.

Try it: watch i hold an int, then a string. The describe function prints the value and type each time.

main.go ▶ Run in Playground 
package main

import "fmt"

func main() {
	var i interface{}
	describe(i)

	i = 42
	describe(i)

	i = "hello"
	describe(i)
}

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