Golang method expressions satisfy function types

methodasfunc.go

package main

import "fmt"

// GreetingFunc builds a greeting from a name.
type GreetingFunc func(string) string

// Formatted builds a greeting based on a printf-style format string.
type Formatted struct {
	Format string
}

// Greeting returns a greeting to who based on the format string.
func (f *Formatted) Greeting(who string) string {
	return fmt.Sprintf(f.Format, who)
}

func main() {
	f := &Formatted{
		Format: "Hello, %s!",
	}
	// Note the method f.Greeting has type GreetingFunc
	var g GreetingFunc = f.Greeting
	fmt.Println(g("World"))
}