https://tour.golang.org/methods/11

readers.go

package main

import "code.google.com/p/go-tour/reader"

type MyReader struct{}

func (reader *MyReader) Read(b []byte )(n int, e error) {
	for i:=0; i< len(b); i++ {
		b[i] = 'A'
	}
	return int(len(b)), nil
}

func main() {
	reader.Validate(&MyReader{})
}