C++模板进阶：从特化到元编程
好的，下面将深入讲解C++模板的进阶特性：
一、模板特化
模板特化允许为特定类型提供定制化的实现：
// 通用模板
template
class MyClass {
public:
void print() {
cout << "Generic implementation" << endl;
}
};
// 全特化：针对 int 类型
template<>
class MyClass {
public:
void print() {
cout << "Specialized for int" << endl;
}
};
偏特化（部分特化）
针对特定类型组合或指针等场景：
// 通用模板
template
class Pair { /*...*/ };
// 偏特化：当两个类型相同时
template
class Pair { /*...*/ };
// 偏特化：针对指针类型
template
class Pair { /*...*/ };
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二、可变参数模板（Variadic Templates）
用于处理任意数量、任意类型的参数：
template
void printAll(Args... args) {
// 递归展开参数包
(cout << ... << args) << endl; // C++17折叠表达式
}
参数包展开技巧
- 递归展开：
template
void print(T t) {
cout << t << endl;
}
template
void print(T t, Args... args) {
cout << t << " ";
print(args...); // 递归调用
}
- sizeof... 运算符：
template
void countArgs(Args... args) {
cout << "Count: " << sizeof...(Args) << endl;
}
三、SFINAE（Substitution Failure Is Not An Error）
利用模板替换失败实现编译期条件判断：
template
enable_if_t, void> process(T val) {
cout << "Processing integral: " << val << endl;
}
template
enable_if_t, void> process(T val) {
cout << "Processing float: " << val << endl;
}
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四、模板元编程（Template Metaprogramming）
在编译期执行计算：
// 编译期计算阶乘
template
struct Factorial {
static constexpr int value = N * Factorial::value;
};
template<>
struct Factorial<0> {
static constexpr int value = 1;
};
// 使用
constexpr int val = Factorial<5>::value; // 编译期得到120
五、模板别名（Alias Templates）
简化复杂类型声明：
template
using Vec = std::vector>; // 自定义分配器
Vec myVec; // 等价于 std::vector>
六、约束模板（C++20 Concepts）
增强模板的类型约束能力：
template
concept Integral = std::is_integral_v; // 定义概念
template // 使用概念约束
T add(T a, T b) {
return a + b;
}
关键注意事项
- 编译期实例化：模板在编译时生成具体代码，可能增加编译时间
- 代码膨胀：过多特化或实例化会导致二进制文件体积增大
- 调试复杂性：错误信息可能冗长难懂（可使用
static_assert提前校验）
通过灵活组合这些特性，可构建高度泛化且类型安全的代码结构，例如：
- 标准库中的
std::tuple,std::function - 策略模式与类型擦除的实现
- 编译期多态与表达式模板优化
若有具体场景需求，可进一步探讨实现方案。
