functional options

package main

import (
	"fmt"
)

type thing struct {
	val string
}

type Option interface {
	apply(*thing)
}

type optionFn func(*thing)

func (fn optionFn) apply(t *thing) { fn(t) }

func newOpt(s string) Option {
	return optionFn(func(t *thing) {
		t.val = s
	})
}

func main() {
	t := &thing{"old"}

	fmt.Println(t)

	fn := newOpt("new")

	fn.apply(t)

	fmt.Println(t)
}