How to dependency inject for a function in go

clients.go

package main

import "fmt"

func handle(f func(input string) string) { fmt.Println(f("foo")) }

func main() {
	handle(func(input string) string {
		return handler(input, &ic{42}, &sc{"bar"})
	})
}

func handler(input string, i intClient, s stringClient) string {
	return fmt.Sprintf("%s: %s %d\n", s.String(), input, i.Int())
}

type intClient interface {
	Int() int
}

type ic struct {
	ret int
}

func (i *ic) Int() int {
	return i.ret
}

type stringClient interface {
	String() string
}

type sc struct {
	ret string
}

func (s *sc) String() string {
	return s.ret
}

functional.go

package main

import "fmt"

func handle(f func(input string) string) { fmt.Println(f("foo")) }

func main() {
	handle(func(input string) string {
		return handler(input, inter(42), stringer("bar"))
	})
}

func handler(input string, intreader func() int, stringreader func() string) string {
	return fmt.Sprintf("%s: %s %d\n", stringreader(), input, intreader())
}

func inter(i int) func() int {
	return func() int {
		return i
	}
}

func stringer(s string) func() string {
	return func() string {
		return s
	}
}

handler.go

package main

import "fmt"

func handle(f func(input string) string) { fmt.Println(f("foo")) }

func main() {
	handle(NewHandler(42, "bar").DoIt)
}

type handler {
	i intClient
	s stringClient
}

func (h *handler) DoIt(input string) string {
	return fmt.Sprintf("%s: %s %d\n", h.s.String(), input, h.i.Int())
}

func NewHandler(i int, s string) {
	return &handler{
		i: &ic{i},
		s: &sc{s},
	}
}

type intClient interface {
	Int() int
}

type ic struct {
	ret int
}

func (i *ic) Int() int {
	return i.ret
}

type stringClient interface {
	String() string
}

type sc struct {
	ret string
}

func (s *sc) String() string {
	return s.ret
}