测试_第10章_模板与泛型.cpp

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编译运行：clang++ -std=c++26 -Wall -Wextra -pthread 测试_第10章_模板与泛型.cpp -o t && ./t（需先 cd 测试/）

// 第10章测试：模板与泛型
#include <print>
#include <string>
#include <type_traits>
#include <concepts>

int failures = 0;
#define CHECK(expr)                                                         \
    do {                                                                    \
        if (!(expr)) {                                                      \
            ++failures;                                                     \
            std::println("FAIL 第{}行: {}", __LINE__, #expr);              \
        }                                                                   \
    } while (0)

// 10.1 函数模板
template <typename T>
T max_of(T a, T b) { return a > b ? a : b; }

// 10.3 类模板
template <typename T>
class Box {
public:
    explicit Box(T value) : value_(std::move(value)) {}
    const T& get() const { return value_; }
private:
    T value_;
};

// 10.4 if constexpr + type traits
template <typename T>
std::string what_kind(const T& v) {
    if constexpr (std::is_pointer_v<T>) {
        return "指针:" + std::to_string(*v);
    } else if constexpr (std::is_same_v<T, std::string>) {
        return "字符串:" + v;
    } else if constexpr (std::is_integral_v<T>) {
        return "整数:" + std::to_string(v);
    } else {
        return "其他";
    }
}

// 10.5 变参模板 + 折叠表达式
template <typename... Ts>
auto sum_all(Ts... args) { return (args + ...); }

template <typename... Ts>
int count_all(Ts... args) { return sizeof...(args); }

// 10.7 concepts
template <std::integral T>
T double_it(T x) { return x * 2; }

template <typename T>
concept HasArea = requires(const T& t) {
    { t.area() } -> std::same_as<double>;
};

template <HasArea T>
double total_area(const T& t) { return t.area(); }

int main() {
    // 10.1
    CHECK(max_of(3, 7) == 7);
    CHECK(max_of(3.5, 2.1) == 3.5);
    CHECK(max_of(std::string("b"), std::string("a")) == "b");

    // 10.3
    Box<int> b1(42);
    Box<std::string> b2("hi");
    CHECK(b1.get() == 42);
    CHECK(b2.get() == "hi");

    // 10.4
    int iv = 5;
    int* pv = &iv;
    std::string sv = "text";
    CHECK(what_kind(pv) == "指针:5");
    CHECK(what_kind(sv) == "字符串:text");
    CHECK(what_kind(iv) == "整数:5");

    // 10.5 折叠
    CHECK(sum_all(1, 2, 3, 4) == 10);
    CHECK(sum_all(1.5, 2.5) == 4.0);
    CHECK(sum_all(std::string("a"), std::string("b"), std::string("c")) == "abc");
    CHECK(count_all(1, 2.5, "x") == 3);

    // 10.7 concepts
    CHECK(double_it(21) == 42);
    // double_it(3.5);  // 编译错误：double 不是 integral

    struct Square { double area() const { return 4.0; } };
    Square sq;
    CHECK(total_area(sq) == 4.0);

    // 10.6 编译期类型检查
    static_assert(std::is_integral_v<int>);
    static_assert(!std::is_integral_v<double>);
    static_assert(std::is_pointer_v<int*>);
    using Plain = std::remove_const_t<const int>;
    static_assert(std::is_same_v<Plain, int>);

    if (failures == 0) std::println("全部通过");
    return failures;
}