C++ 设计模式-策略模式

支付策略

#include <iostream>
#include <memory>
#include <unordered_map>
#include <vector>
#include <ctime>// 基础策略接口
class PaymentStrategy {
public:virtual ~PaymentStrategy() = default;virtual std::string name() const = 0;virtual bool validate(double amount, const std::string& currency) const = 0;virtual void pay(double amount, const std::string& currency) const = 0;virtual double calculate_fee(double amount) const = 0;
};// 策略工厂系统
class StrategyFactory {
public:using StrategyCreator = std::function<std::unique_ptr<PaymentStrategy>()>;static StrategyFactory& instance() {static StrategyFactory instance;return instance;}void register_strategy(const std::string& id, StrategyCreator creator) {creators_[id] = creator;}std::unique_ptr<PaymentStrategy> create(const std::string& id) const {if (auto it = creators_.find(id); it != creators_.end()) {return it->second();}return nullptr;}std::vector<std::string> available_strategies() const {std::vector<std::string> names;for (const auto& [id, _] : creators_) {names.push_back(id);}return names;}private:std::unordered_map<std::string, StrategyCreator> creators_;
};// 自动注册宏
#define REGISTER_PAYMENT_STRATEGY(StrategyClass, strategy_id) \namespace { \struct AutoRegister_##StrategyClass { \AutoRegister_##StrategyClass() { \StrategyFactory::instance().register_strategy( \strategy_id, \[]{ return std::make_unique<StrategyClass>(); } \); \} \}; \AutoRegister_##StrategyClass auto_reg_##StrategyClass; \}// 微信支付策略
class WechatPayStrategy : public PaymentStrategy {const double max_amount_ = 50000.0; // 单笔最大金额public:std::string name() const override { return "WeChat Pay"; }bool validate(double amount, const std::string& currency) const override {return currency == "CNY" && amount <= max_amount_;}void pay(double amount, const std::string& currency) const override {std::cout << "微信支付成功\n"<< "金额: ¥" << amount << "\n"<< "请在小程序确认支付" << std::endl;}double calculate_fee(double amount) const override {return amount * 0.001; // 0.1%手续费}
};
REGISTER_PAYMENT_STRATEGY(WechatPayStrategy, "wechat_pay");// PayPal策略
class PayPalStrategy : public PaymentStrategy {const std::vector<std::string> supported_currencies_{"USD", "EUR", "GBP"};public:std::string name() const override { return "PayPal"; }bool validate(double amount, const std::string& currency) const override {return std::find(supported_currencies_.begin(), supported_currencies_.end(), currency) != supported_currencies_.end();}void pay(double amount, const std::string& currency) const override {std::cout << "Processing PayPal payment\n"<< "Amount: " << currency << " " << amount << "\n"<< "Redirecting to PayPal login..." << std::endl;}double calculate_fee(double amount) const override {return std::max(0.3, amount * 0.05); // 5% + $0.3}
};
REGISTER_PAYMENT_STRATEGY(PayPalStrategy, "paypal");// 比特币策略（带实时汇率）
class BitcoinStrategy : public PaymentStrategy {// 模拟实时汇率获取double get_bitcoin_price() const {static const double BASE_PRICE = 45000.0; // 基础价格// 模拟价格波动return BASE_PRICE * (1.0 + 0.1 * sin(time(nullptr) % 3600));}public:std::string name() const override { return "Bitcoin"; }bool validate(double amount, const std::string& currency) const override {return currency == "BTC" || currency == "USD";}void pay(double amount, const std::string& currency) const override {if (currency == "USD") {double btc_amount = amount / get_bitcoin_price();std::cout << "Converting USD to BTC: " << "₿" << btc_amount << std::endl;amount = btc_amount;}std::cout << "区块链交易确认中...\n"<< "转账金额: ₿" << amount << "\n"<< "预计确认时间: 10分钟" << std::endl;}double calculate_fee(double amount) const override {return 0.0001 * get_bitcoin_price(); // 固定矿工费}
};
REGISTER_PAYMENT_STRATEGY(BitcoinStrategy, "bitcoin");// 支付处理器
class PaymentProcessor {std::unordered_map<std::string, std::unique_ptr<PaymentStrategy>> strategies_;public:void load_strategy(const std::string& id) {if (auto strategy = StrategyFactory::instance().create(id)) {strategies_[id] = std::move(strategy);}}void process_payment(const std::string& currency, double amount) {auto strategy = select_strategy(currency, amount);if (!strategy) {throw std::runtime_error("No available payment method");}std::cout << "\n=== 支付方式: " << strategy->name() << " ==="<< "\n金额: " << currency << " " << amount<< "\n手续费: " << strategy->calculate_fee(amount)<< "\n-------------------------" << std::endl;strategy->pay(amount, currency);}private:PaymentStrategy* select_strategy(const std::string& currency, double amount) {// 选择优先级：本地支付 > 国际支付 > 加密货币for (auto& [id, strategy] : strategies_) {if (id == "wechat_pay" && strategy->validate(amount, currency)) {return strategy.get();}}for (auto& [id, strategy] : strategies_) {if (id == "alipay" && strategy->validate(amount, currency)) {return strategy.get();}}for (auto& [id, strategy] : strategies_) {if (strategy->validate(amount, currency)) {return strategy.get();}}return nullptr;}
};// 使用示例
int main() {PaymentProcessor processor;// 加载所有注册的支付方式for (const auto& id : StrategyFactory::instance().available_strategies()) {processor.load_strategy(id);}// 人民币支付try {processor.process_payment("CNY", 200.0);processor.process_payment("CNY", 60000.0); // 应触发异常} catch (const std::exception& e) {std::cerr << "支付失败: " << e.what() << std::endl;}// 美元支付processor.process_payment("USD", 500.0);// 比特币支付processor.process_payment("BTC", 0.1);processor.process_payment("USD", 1000.0); // 自动转换为BTCreturn 0;
}

代码解析

策略扩展机制

REGISTER_PAYMENT_STRATEGY(WechatPayStrategy, "wechat_pay");

自动注册：通过宏实现新策略的零配置接入
唯一标识：每个策略有唯一的注册ID（如wechat_pay）

微信支付实现

class WechatPayStrategy : public PaymentStrategy {bool validate(...) { /* 校验人民币 */ }void pay(...) { /* 微信特有流程 */ }
};

本地化支持：仅接受人民币
移动支付流程：模拟小程序支付场景

PayPal国际支付

class PayPalStrategy : public PaymentStrategy {bool validate(...) { /* 支持多币种 */ }void pay(...) { /* 跳转PayPal */ }
};

多币种支持：USD/EUR/GBP
典型手续费模型：固定费用+百分比

比特币支付

class BitcoinStrategy : public PaymentStrategy {double get_bitcoin_price() { /* 模拟实时价格 */ }void pay(...) { /* 自动转换法币 */ }
};

加密货币支持：直接接受BTC或自动转换USD
动态手续费：基于当前币价计算矿工费

智能策略选择

PaymentStrategy* select_strategy(...) {// 优先选择本地支付方式// 次选国际支付// 最后考虑加密货币
}

业务优先级：体现支付方式选择策略
动态路由：根据金额和币种自动路由

执行结果示例

=== 支付方式: WeChat Pay ===
金额: CNY 200
手续费: 0.2
-------------------------
微信支付成功
金额: ¥200
请在小程序确认支付支付失败: No available payment method=== 支付方式: PayPal ===
金额: USD 500
手续费: 25.3
-------------------------
Processing PayPal payment
Amount: USD 500
Redirecting to PayPal login...=== 支付方式: Bitcoin ===
金额: BTC 0.1
手续费: 4.5
-------------------------
区块链交易确认中...
转账金额: ₿0.1
预计确认时间: 10分钟=== 支付方式: Bitcoin ===
金额: USD 1000
手续费: 4.5
-------------------------
Converting USD to BTC: ₿0.0221132
区块链交易确认中...
转账金额: ₿0.0221132
预计确认时间: 10分钟

待扩展

新增策略步骤：
- 继承PaymentStrategy实现新类
- 实现所有纯虚函数
- 使用REGISTER_PAYMENT_STRATEGY注册

动态配置：

// 示例：从JSON加载策略配置
void load_config(const json& config) {for (auto& item : config["strategies"]) {auto strategy = factory.create(item["id"]);strategy->configure(item["params"]);add_strategy(std::move(strategy));}
}

混合支付：

class SplitPaymentStrategy : public PaymentStrategy {// 支持多个策略分摊支付void pay(...) override {credit_card_->pay(part1, currency);crypto_->pay(part2, currency);}
};