interface-proxy.go

package main 

import "fmt" 

type Ingredient struct {
  Name string 
  Amount float64 
}

type Ingredients interface {
  Name() string 
  GetIngredients() []Ingredient
}

func DisplayDrinkIngredients(drink Ingredients) {
  fmt.Println(drink.Name(), drink.GetIngredients()) 
}

type Drink struct {
  NameFn func() string 
  GetIngredientsFn func() []Ingredient
}

func (d *Drink) Name() string {
  if d.NameFn != nil {
    return d.NameFn()
  }
  return ""
}

func (d *Drink) GetIngredients() []Ingredient {
  if d.GetIngredientsFn != nil {
    return d.GetIngredientsFn()
  }
  return []Ingredient{}
}

func main() {
  beer := &Drink{
    NameFn: func() string { return "beer" },
    GetIngredientsFn: func() []Ingredient { return []Ingredient{{Name: "wheat", Amount: 10.5},{Name: "Yeast", Amount: 1.25}, {Name: "Hops", Amount: 6.0}}},
  }

  water := &Drink{
    NameFn: func() string { return "water" },
  }
  
  DisplayDrinkIngredients(beer)
  DisplayDrinkIngredients(water)
}