Tour of Go 2.0

Interfaces are implemented implicitly

Go interfaces are implicit. There’s no implements keyword — if your type has the right methods, it satisfies the interface. Full stop.

Here, T implements I just by having an M() method. No declaration needed. No link back to the interface.

This matters. It means you can write an interface in one package and have a type in a completely separate package satisfy it — without either package knowing about the other. That’s powerful decoupling.

main.go ▶ Run in Playground 
package main

import "fmt"

type I interface {
	M()
}

type T struct {
	S string
}

// This method means type T implements the interface I,
// but we don't need to explicitly declare that it does so.
func (t T) M() {
	fmt.Println(t.S)
}

func main() {
	var i I = T{"hello"}
	i.M()
}