Go interface example

example.go

// Run at https://play.golang.org/p/gYCGtWOHGci

package main

import (
	"fmt"
)

// Define an interface
type Foo interface {
	Bar() int
}

// Define a struct
type Baz struct {
	Value int
}

// Baz implements Foo interface
func (b *Baz) Bar() int {
	return b.Value * 10
}

// Define another struct
type Bax struct {
	Value int
}

// Define a generic function that accepts Foo interface implementers
func zzz(f Foo) int {
	return f.Bar()
}

func main() {
	// Test that `zzz` works on a Baz value
	f := &Baz{12}
	fmt.Printf("Baz --> %d", zzz(f))

	// `zzz` doesn't work on a Bax value
	// > g := &Bax{14}
	// > fmt.Printf("Bax --> %d", zzz(g))
	// Returns the error:
	// > cannot use g (type *Bax) as type Foo in argument to zzz:
	// >   *Bax does not implement Foo (missing Bar method)
}