Stringers

One of the most ubiquitous interfaces is Stringer defined by the fmt package.

type Stringer interface {
    String() string
}

A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values.

stringer.go

package main
import "fmt"
type Person struct {
    Name string
    Age  int
}
func (p Person) String() string {
    return fmt.Sprintf("%v (%v years)", p.Name, p.Age)
}
func main() {
    a := Person{"Arthur Dent", 42}
    z := Person{"Zaphod Beeblebrox", 9001}
    fmt.Println(a, z)
}