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设计模式九：构建器模式 (Builder Pattern)

news 2025/7/27 15:06:03

动机(Motivation)

1、在软件系统中，有时候面临着“一个复杂对象”的创建工作，其通常由各个部分的子对象用一定的算法构成；由于需求的变化，这个复杂对象的各个部分经常面临着剧烈的变化，但是将它们组合在一起的算法却相对稳定。
2、如何应对这种变化？如何提供一种“封装机制”来隔离出“复杂对象的各个部分”的变化，从而保持系统中的“稳定构建算法”不随着需求改变而改变?

基本概念

定义：构建器模式是一种创建型设计模式，它允许您分步骤创建复杂对象，使得相同的构建过程可以创建不同的表示。

构建器模式的核心思想是将复杂对象的构建与其表示分离，使得：

客户端不需要知道对象内部的具体组成细节
相同的构建过程可以创建不同的表示
可以更精细地控制对象的构建过程

实现方式

1. 经典构建器模式实现

#include <iostream>
#include <memory>
#include <string>// 最终要构建的产品
class Pizza {
public:void setDough(const std::string& dough) {dough_ = dough;}void setSauce(const std::string& sauce) {sauce_ = sauce;}void setTopping(const std::string& topping) {topping_ = topping;}void showPizza() const {std::cout << "Pizza with " << dough_ << " dough, "<< sauce_ << " sauce and "<< topping_ << " topping." << std::endl;}private:std::string dough_;std::string sauce_;std::string topping_;
};// 抽象构建器
class PizzaBuilder {
public:virtual ~PizzaBuilder() = default;Pizza* getPizza() {return pizza_.get();}void createNewPizza() {pizza_ = std::make_unique<Pizza>();}virtual void buildDough() = 0;virtual void buildSauce() = 0;virtual void buildTopping() = 0;protected:std::unique_ptr<Pizza> pizza_;
};// 具体构建器 -  HawaiianPizzaBuilder
class HawaiianPizzaBuilder : public PizzaBuilder {
public:void buildDough() override {pizza_->setDough("cross");}void buildSauce() override {pizza_->setSauce("mild");}void buildTopping() override {pizza_->setTopping("ham+pineapple");}
};// 具体构建器 - SpicyPizzaBuilder
class SpicyPizzaBuilder : public PizzaBuilder {
public:void buildDough() override {pizza_->setDough("pan baked");}void buildSauce() override {pizza_->setSauce("hot");}void buildTopping() override {pizza_->setTopping("pepperoni+salami");}
};// 指导者 (Director) - 控制构建过程
class Cook {
public:void setPizzaBuilder(PizzaBuilder* pb) {pizzaBuilder_ = pb;}Pizza* getPizza() {return pizzaBuilder_->getPizza();}void constructPizza() {pizzaBuilder_->createNewPizza();pizzaBuilder_->buildDough();pizzaBuilder_->buildSauce();pizzaBuilder_->buildTopping();}private:PizzaBuilder* pizzaBuilder_;
};int main() {Cook cook;// 构建 Hawaiian PizzaHawaiianPizzaBuilder hawaiianBuilder;cook.setPizzaBuilder(&hawaiianBuilder);cook.constructPizza();Pizza* hawaiianPizza = cook.getPizza();hawaiianPizza->showPizza();  // 输出: Pizza with cross dough, mild sauce and ham+pineapple topping.// 构建 Spicy PizzaSpicyPizzaBuilder spicyBuilder;cook.setPizzaBuilder(&spicyBuilder);cook.constructPizza();Pizza* spicyPizza = cook.getPizza();spicyPizza->showPizza();  // 输出: Pizza with pan baked dough, hot sauce and pepperoni+salami topping.return 0;
}

2. 流式接口构建器 (更现代的C++实现)

#include <iostream>
#include <memory>
#include <string>class Computer {
public:void setCPU(const std::string& cpu) { cpu_ = cpu; }void setRAM(const std::string& ram) { ram_ = ram; }void setStorage(const std::string& storage) { storage_ = storage; }void setGPU(const std::string& gpu) { gpu_ = gpu; }void showSpecs() const {std::cout << "Computer Specs:\n"<< "CPU: " << cpu_ << "\n"<< "RAM: " << ram_ << "\n"<< "Storage: " << storage_ << "\n"<< "GPU: " << (gpu_.empty() ? "Integrated" : gpu_) << "\n";}private:std::string cpu_;std::string ram_;std::string storage_;std::string gpu_;
};class ComputerBuilder {
public:ComputerBuilder() : computer_(std::make_unique<Computer>()) {}ComputerBuilder& setCPU(const std::string& cpu) {computer_->setCPU(cpu);return *this;}ComputerBuilder& setRAM(const std::string& ram) {computer_->setRAM(ram);return *this;}ComputerBuilder& setStorage(const std::string& storage) {computer_->setStorage(storage);return *this;}ComputerBuilder& setGPU(const std::string& gpu) {computer_->setGPU(gpu);return *this;}std::unique_ptr<Computer> build() {return std::move(computer_);}private:std::unique_ptr<Computer> computer_;
};int main() {// 使用流式接口构建计算机auto gamingPC = ComputerBuilder().setCPU("Intel i9-13900K").setRAM("32GB DDR5").setStorage("2TB NVMe SSD").setGPU("NVIDIA RTX 4090").build();gamingPC->showSpecs();auto officePC = ComputerBuilder().setCPU("AMD Ryzen 5").setRAM("16GB DDR4").setStorage("512GB SSD").build();  // 没有设置GPUofficePC->showSpecs();return 0;
}