创建型-👷建造者模式（Builder Pattern）

建造者模式（Builder Pattern）是一种创建型设计模式，它允许你逐步构造一个复杂对象，将构造过程和表示分离，从而可以创建具有不同属性组合的对象。

在Go语言中，你可以使用结构体和方法来实现建造者模式。

就想你去麦当劳 Or KFC点餐～ 你可以任意单点餐品，也可以选择不同餐品搭配的套餐！

但是每一种餐品都是单独制作出来的，将不同的单品搭配起来，就是不同的套餐了！

构建了两种不同类型的套餐，每种套餐都包含主餐、饮品和甜品小食。

package main

import "fmt"

// Product 表示点餐的餐点
type Product struct {
	mainDish string // 主餐
	drink    string // 饮品
	dessert  string // 甜品小食
}

// Builder 接口定义了构建餐点的方法
type Builder interface {
	BuildMainDish(MainDish string) Builder
	BuildDrink(Drink string) Builder
	BuildDessert(Dessert string) Builder
	GetProduct() Product
}

// ProductPackage 表示由 Product 三件套组成的套餐！
type ProductPackage struct {
	product Product
}

func (b *ProductPackage) BuildMainDish(MainDish string) Builder {
	b.product.mainDish = MainDish // 主菜是猪柳蛋汉堡
	// 建造者方法可以返回建造者自身，这样可以支持链式调用，使代码更简洁
	return b
}

func (b *ProductPackage) BuildDrink(Drink string) Builder {
	b.product.drink = Drink // 饮料
	return b
}

func (b *ProductPackage) BuildDessert(Dessert string) Builder {
	b.product.dessert = Dessert // 小食
	return b
}

func (b *ProductPackage) GetProduct() Product {
	return b.product
}

// 猪柳蛋麦满分套餐
type PorkTenderloinEggMcMuff struct {
	builder Builder
}

func (d *PorkTenderloinEggMcMuff) Do() Product {
	return d.builder.
		BuildMainDish("PorkTenderloinEgg Burger").
		BuildDrink("咖啡").
		BuildDessert("紫薯饼").
		GetProduct()
}

// 大脆鸡扒麦满分
type BigCrispyChickenChopWheat struct {
	builder Builder
}

func (d *BigCrispyChickenChopWheat) Do() Product {
	return d.builder.
		BuildMainDish("BigCrispyChickenChopWheat Burger").
		BuildDrink("豆浆").
		BuildDessert("薯饼").
		GetProduct()
}
func main() {
	builder := &ProductPackage{}
	porkTenderloinEggPkg := &PorkTenderloinEggMcMuff{builder: builder}
	bigCrispyChickenChopWheat := &BigCrispyChickenChopWheat{builder: builder}
	PorkTenderloinEggMcMuffMeal := porkTenderloinEggPkg.Do()
  
	fmt.Println(" ============= 猪柳蛋麦满分 ========== ")
	bigCrispyChickenChopWheatMeal := bigCrispyChickenChopWheat.Do()
	fmt.Printf("Main Dish: %s\n", PorkTenderloinEggMcMuffMeal.mainDish)
	fmt.Printf("Drink: %s\n", PorkTenderloinEggMcMuffMeal.drink)
	fmt.Printf("Dessert: %s\n", PorkTenderloinEggMcMuffMeal.dessert)
  
	fmt.Println(" ========== 大脆鸡扒麦满分 ========== ")
	fmt.Printf("Main Dish: %s\n", bigCrispyChickenChopWheatMeal.mainDish)
	fmt.Printf("Drink: %s\n", bigCrispyChickenChopWheatMeal.drink)
	fmt.Printf("Dessert: %s\n", bigCrispyChickenChopWheatMeal.dessert)
}

代码中使用了不同的建造者实现来构建不同类型的套餐，然后通过调用各自的 Do 方法进行构建

使用建造者模式构建不同类型的套餐，每种套餐都由主餐、饮品和甜品小食组成。通过使用不同的建造者实现，可以灵活地构建不同的套餐组合

后续如果对套餐进行扩展，直接在产品新增品类，在Buider中新增新产品的制作方法就可以了

// Product 表示点餐的餐点
type Product struct {
	mainDish string // 主餐
	drink    string // 饮品
	dessert  string // 甜品小食

+	Toy string // 玩具
}

// Builder 接口定义了构建餐点的方法
type Builder interface {
	BuildMainDish(MainDish string) Builder
	BuildDrink(Drink string) Builder
	BuildDessert(Dessert string) Builder
+	BuildToy(Toy string) Builder
	GetProduct() Product
}

定义儿童套餐

// 儿童欢乐套餐
type ChildHappyPackage struct {
	builder Builder
}

func (d *ChildHappyPackage) Do() Product {
	return d.builder.
		BuildMainDish("ChildHappyPackage Burger").
		BuildDrink("牛奶").
		BuildDessert("薯条").
		BuildToy("变形金刚").
		GetProduct()
}

func main() {
	builder := &ProductPackage{}
	porkTenderloinEggPkg := &PorkTenderloinEggMcMuff{builder: builder}
	bigCrispyChickenChopWheat := &BigCrispyChickenChopWheat{builder: builder}
	PorkTenderloinEggMcMuffMeal := porkTenderloinEggPkg.Do()
	bigCrispyChickenChopWheatMeal := bigCrispyChickenChopWheat.Do()
	fmt.Println(" ============= 猪柳蛋麦满分 ========== ")
	fmt.Printf("Main Dish: %s\n", PorkTenderloinEggMcMuffMeal.mainDish)
	fmt.Printf("Drink: %s\n", PorkTenderloinEggMcMuffMeal.drink)
	fmt.Printf("Dessert: %s\n", PorkTenderloinEggMcMuffMeal.dessert)
	fmt.Println(" ========== 大脆鸡扒麦满分 ========== ")
	fmt.Printf("Main Dish: %s\n", bigCrispyChickenChopWheatMeal.mainDish)
	fmt.Printf("Drink: %s\n", bigCrispyChickenChopWheatMeal.drink)
	fmt.Printf("Dessert: %s\n", bigCrispyChickenChopWheatMeal.dessert)
+	fmt.Println(" ========== 欢乐儿童套餐 ========== ")
+	childHappyPackage := &ChildHappyPackage{builder: builder}
+	childHappyPackageMeal := childHappyPackage.Do()
+	fmt.Printf("Main Dish: %s\n", childHappyPackageMeal.mainDish)
+	fmt.Printf("Drink: %s\n", childHappyPackageMeal.drink)
+	fmt.Printf("Dessert: %s\n", childHappyPackageMeal.dessert)
+	fmt.Printf("Dessert: %s\n", childHappyPackageMeal.Toy)
}