cep21

package item

type Item struct {
  Price float64
}

cep21

package cart

import "customer"
import "item"

type Client struct {
}

func (c *Client) Purchase(who *customer.User, what *item.Item) {
}

cep21

package customer

import "item"

type User struct {
  Name string
}

type Item => item.Item

cep21

package cart

type Cart struct {
}

func (c *Cart) Subtotal() float64 {
	// calculate and return
}

cep21

package store

import "cart"

type Store struct {
}

func (s *Store) RenderPage(c *cart.Cart) {
	// Do thing with total
}

cep21

package store

type Totaller interface {
	Subtotal() float64
}

type Store struct {
}

func (s *Store) RenderPage(t Totaller) {

cep21

package news

import "store"

type Totaller interface {
	Subtotal() float64
}

type NewsfeedRenderable struct {}

cep21

package news

type Totaller interface {
	Subtotal() float64
}

type NewsfeedRenderable struct {}

func (n *NewsfeedRenderable) RenderPage(t Totaller) {

cep21

package app

type Totaller interface {
	Subtotal() float64
}

type Renderable interface {
	RenderPage(t Totaller)
}

cep21

package main

import (
	"app"
	"store"
)

func main( {
//	./store_main.go:9: cannot use Store literal (type *Store) as type app.Renderable in argument to app.RunApplication:
//		*Store does not implement app.Renderable (wrong type for RenderPage method)