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Interfaces

englishBot and spanishBot both implement the getGreeting method so according to bot interface, they are both of considered interfaces.

package main
import "fmt"

// Declare interface 
type bot interface {
  getGreeting() string
}

type spanishBot struct{}
type englishBot struct{}

func main() {
  eb := englishBot{}
  sb := spanishBot{}
  
  printGreeting(eb)
  printGreeting(sb)
}


// Declare that function uses interface
func printGreeting(b bot) {
  fmt.Println(b.getGreeting())
}

func (englishBot) getGreeting() string {
  return "Hi there!"
}

func (spanishBot) getGreeting() string {
  return "Hola!"
}

  • Interfaces are not generic types.
  • Interfaces are implicit (no need to implements a certain type to the interface type)
  • Are a contract to help us manage types.

Reader Interface and io.Copy​

Very useful interface is the Reader which takes in any source of information (i.e. HTTP response body, text/image file on disk, user input) and outputs a byteslice ([]byte).

To read data from an HTTP source:

resp, err := http.Get("https://httpbin.org/anything")
if err != nil {
  print(err)
}

// resp.Body implements the `Reader` interface
// os.Stdout implments the `Wrtier` interface
io.Copy(os.Stdout, resp.Body)