建造者模式通过分离复杂对象的构建与表示，使同一构建过程可创建不同配置的Computer对象，提升代码可读性与维护性。
建造者模式用于分离复杂对象的构建和表示，使得同样的构建过程可以创建不同的表示。在C++中，当一个类的构造函数参数过多，或者对象的构建步骤较复杂、存在多种变体时，使用建造者模式能显著提升代码可读性和可维护性。
建造者模式的核心思想
将对象的构建逻辑从构造函数中剥离出来，通过一个独立的Builder类逐步配置和组装对象。最终通过build()方法生成目标对象。这种方式避免了“伸缩构造器反模式”（telescoping constructors），即写多个参数不同的构造函数。
比如我们要构建一个复杂的Computer类，包含CPU、内存、硬盘、显卡等组件，不同配置组合多样。
基本实现结构
定义产品类、抽象建造者、具体建造者和指挥者（可选）。
示例代码：
#include <iostream>
#include <string>
// 1. 产品类：Computer
class Computer {
public:
void setCPU(const std::string& cpu) { m_cpu = cpu; }
void setRAM(const std::string& ram) { m_ram = ram; }
void setStorage(const std::string& storage) { m_storage = storage; }
void setGPU(const std::string& gpu) { m_gpu = gpu; }
void show() const {
std::cout << "Computer Config:\n";
std::cout << " CPU: " << m_cpu << "\n";
std::cout << " RAM: " << m_ram << "\n";
std::cout << " Storage: " << m_storage << "\n";
std::cout << " GPU: " << m_gpu << "\n";
}
private:
std::string m_cpu;
std::string m_ram;
std::string m_storage;
std::string m_gpu;
};
// 2. 抽象建造者
class ComputerBuilder {
public:
virtual ~ComputerBuilder() = default;
virtual void buildCPU() = 0;
virtual void buildRAM() = 0;
virtual void buildStorage() = 0;
virtual void buildGPU() = 0;
virtual Computer* getComputer() = 0;
};
// 3. 具体建造者：游戏电脑
class GamingComputerBuilder : public ComputerBuilder {
public:
GamingComputerBuilder() { m_computer = new Computer(); }
void buildCPU() override { m_computer->setCPU("Intel i9"); }
void buildRAM() override { m_computer->setRAM("32GB DDR5"); }
void buildStorage() override { m_computer->setStorage("1TB NVMe SSD"); }
void buildGPU() override { m_computer->setGPU("RTX 4090"); }
Computer* getComputer() override {
Computer* temp = m_computer;
m_computer = nullptr;
return temp;
}
~GamingComputerBuilder() {
delete m_computer;
}
private:
Computer* m_computer;
};
// 4. 具体建造者：办公电脑
class OfficeComputerBuilder : public ComputerBuilder {
public:
OfficeComputerBuilder() { m_computer = new Computer(); }
void buildCPU() override { m_computer->setCPU("Intel i5"); }
void buildRAM() override { m_computer->setRAM("16GB DDR4"); }
void buildStorage() override { m_computer->setStorage("512GB SATA SSD"); }
void buildGPU() override { m_computer->setGPU("Integrated Graphics"); }
Computer* getComputer() override {
Computer* temp = m_computer;
m_computer = nullptr;
return temp;
}
~OfficeComputerBuilder() {
delete m_computer;
}
private:
Computer* m_computer;
};
// 5. 指挥者（可选）
class Director {
public:
void setBuilder(ComputerBuilder* builder) { m_builder = builder; }
Computer* construct() {
m_builder->buildCPU();
m_builder->buildRAM();
m_builder->buildStorage();
m_builder->buildGPU();
return m_builder->getComputer();
}
private:
ComputerBuilder* m_builder;
};使用方式
通过Director控制构建流程，或直接调用Builder的各个步骤。
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int main() {
Director director;
GamingComputerBuilder gamingBuilder;
OfficeComputerBuilder officeBuilder;
// 构建游戏电脑
director.setBuilder(&gamingBuilder);
Computer* gamingPC = director.construct();
gamingPC->show();
std::cout << "\n";
// 构建办公电脑
director.setBuilder(&officeBuilder);
Computer* officePC = director.construct();
officePC->show();
delete gamingPC;
delete officePC;
return 0;
}现代C++中的流式建造者（Fluent Builder）
更符合C++习惯的方式是使用链式调用，提升API易用性。
class Computer {
public:
Computer& cpu(const std::string& c) { m_cpu = c; return *this; }
Computer& ram(const std::string& r) { m_ram = r; return *this; }
Computer& storage(const std::string& s) { m_storage = s; return *this; }
Computer& gpu(const std::string& g) { m_gpu = g; return *this; }
void show() const {
std::cout << "Custom Computer:\n";
std::cout << " CPU: " << m_cpu << "\n";
std::cout << " RAM: " << m_ram << "\n";
std::cout << " Storage: " << m_storage << "\n";
std::cout << " GPU: " << m_gpu << "\n";
}
private:
std::string m_cpu;
std::string m_ram;
std::string m_storage;
std::string m_gpu;
};
// 使用示例
/*
Computer myPC;
myPC.cpu("AMD Ryzen 7")
.ram("32GB")
.storage("2TB SSD")
.gpu("RTX 4070")
.show();
*/这种风格简洁直观，适合配置类对象，广泛应用于现代C++库设计中。
基本上就这些。根据实际需求选择传统建造者或流式接口，关键是把复杂构建逻辑封装好，让使用者专注配置而非细节。
