Go 2 Generics -- https://go2goplay.golang.org/p/vW7-88vRFzj

simple.go

package main

import (
	"fmt"
)

func main() {
	fmt.Printf("%#v\n", Identity('a'))
	fmt.Printf("%#v\n", Identity(Box('a')))
	fmt.Printf("%#v\n", Identity(Unbox(Box('a'))))
	fmt.Printf("%#v\n", Apply(Identity(rune), 'a'))
}

// Identity function
func Identity(type A)(id A) A { return id }

// Ref cell for boxing values
type Ref(type A) struct{ value *A }

// Box a value
func Box(type A)(value A) Ref(A) { return Ref(A){&value} }

// Unbox a value
func Unbox(type A)(box Ref(A)) A { return *box.value }

// Apply a function to an arg
func Apply(type A, B)(f func(A) B, a A) B { return f(a) }