main.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"text/tabwriter"
)

type Beatle struct {
	Name       string
	Instrument string
	Quote      string
}

func (b Beatle) String() string {
	return fmt.Sprintf("%s plays %s", b.Name, b.Instrument)
}

func (b Beatle) GoString() string {
	bb := &bytes.Buffer{}
	bb.WriteString("Beatle{\n")

	w := tabwriter.NewWriter(bb, 0, 0, 1, ' ', tabwriter.TabIndent)
	fmt.Fprintf(bb, "\tName:\t\t%s\n", b.Name)
	fmt.Fprintf(bb, "\tInstrument:\t%s\n", b.Instrument)
	fmt.Fprintf(bb, "\tQuote:\t\t%s\n", b.Quote)
	w.Flush()

	bb.WriteString("}")
	return bb.String()
}

func (b Beatle) Format(s fmt.State, verb rune) {
	switch verb {
	case 'v':
		if s.Flag('#') {
			fmt.Fprint(s, b.GoString())
			return
		}
		if s.Flag('+') {
			m := map[string]Beatle{
				fmt.Sprintf("%T", b): b,
			}
			json.NewEncoder(s).Encode(m)
			return
		}
		json.NewEncoder(s).Encode(b)
	case 'q':
		fmt.Fprintf(s, "%s said %s", b.Name, b.Quote)
	default:
		fmt.Fprint(s, b.String())
	}
}

func main() {
	b := Beatle{
		Name:       "John",
		Instrument: "Guitar",
		Quote:      "Imagine all the people",
	}

	fmt.Printf("%#v\n", b)

}