init-import.go

/* start prcess/process.go */
package process

var Fetch Fetch // Gobal variable, but no initilize, and For Extension!!!

func Process(x string) {
   fetch.Fetch(x)
}
/* end prcess/process.go */

/* start fetch/fetch.go */
package fetch

type Fetch interface {
    Fetch(x string)
}
/* end fetch/fetch.go */

/* start fetch/http/http.go */

// extract http sub-package
package http

type httpFetch struct {
}

// ............

func NewHttpFetch() Fetch {
     return &httpFetch
}
/* end fetch/http/http.go */

func init() { 
// use `http.init` to inject http itself into `proces.fetch` field.
     process.Fetch = &httpFetch{}
}

/* start main.go */
package main

// just wire http up us import statement.
import _ "fetch/http" 

func main() {
    process.Process("11211")
}
/* end main.go */