feat: volumn 4, templated programmings

README.md

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 ---
 
 <!-- COVERAGE_START -->
-![English Coverage](https://img.shields.io/badge/en_coverage-100%25-green.svg) 592/594 docs translated
+![English Coverage](https://img.shields.io/badge/en_coverage-100%25-green.svg) 602/604 docs translated
 <!-- COVERAGE_END -->
 
 ## 这是什么项目

code/examples/vol4/vol1-basics-cpp11-14/comparable_mixin.cpp

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+// Comparable<Derived>:CRTP mixin,只实现 < 和 ==,自动补齐 > <= >= !=
+// 对应文章:documents/vol4-advanced/vol1-basics-cpp11-14/09-crtp.md
+// 编译:g++ -Wall -Wextra -std=c++20 comparable_mixin.cpp -o comparable && ./comparable
+#include <iostream>
+
+template <typename Derived> struct Comparable {
+    friend bool operator>(const Derived& a, const Derived& b) { return b < a; }
+    friend bool operator<=(const Derived& a, const Derived& b) { return !(b < a); }
+    friend bool operator>=(const Derived& a, const Derived& b) { return !(a < b); }
+    friend bool operator!=(const Derived& a, const Derived& b) { return !(a == b); }
+};
+
+struct Point : Comparable<Point> {
+    int x, y;
+    Point(int x_, int y_) : x(x_), y(y_) {}
+    // 只实现 < 和 ==,其余四个由 Comparable<Point> 自动补齐
+    friend bool operator<(const Point& a, const Point& b) { return a.x < b.x; }
+    friend bool operator==(const Point& a, const Point& b) { return a.x == b.x; }
+};
+
+int main() {
+    Point p1{1, 2}, p2{3, 4};
+    std::cout << std::boolalpha;
+    std::cout << "p1 < p2:  " << (p1 < p2) << "\n";
+    std::cout << "p1 > p2:  " << (p1 > p2) << "\n";
+    std::cout << "p1 <= p2: " << (p1 <= p2) << "\n";
+    std::cout << "p1 >= p2: " << (p1 >= p2) << "\n";
+    std::cout << "p1 != p2: " << (p1 != p2) << "\n";
+    return 0;
+}

code/examples/vol4/vol1-basics-cpp11-14/crtp_static_polymorphism.cpp

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+// CRTP 静态多态:派生类把自己传给基类,编译期绑定,无 vtable 无运行时分派
+// 对应文章:documents/vol4-advanced/vol1-basics-cpp11-14/09-crtp.md
+// 编译运行:g++ -Wall -Wextra -std=c++20 crtp_static_polymorphism.cpp -o crtp && ./crtp
+// 看零开销汇编:g++ -O2 -std=c++20 -DCRTP_BENCH -S crtp_static_polymorphism.cpp -o crtp.s
+//   use_crtp() 会被完全内联成 mov $0x2a,%eax; ret(对比虚函数版的 vtable 解引用)
+#include <iostream>
+
+template <typename Derived> struct Shape {
+    const char* name() { return static_cast<Derived*>(this)->name_impl(); }
+    double area() { return static_cast<Derived*>(this)->area_impl(); }
+};
+
+struct Circle : Shape<Circle> {
+    double r;
+    explicit Circle(double r_) : r(r_) {}
+    const char* name_impl() { return "Circle"; }
+    double area_impl() { return 3.14159 * r * r; }
+};
+
+struct Square : Shape<Square> {
+    double side;
+    explicit Square(double s) : side(s) {}
+    const char* name_impl() { return "Square"; }
+    double area_impl() { return side * side; }
+};
+
+#ifdef CRTP_BENCH
+// 汇编基准:use_crtp 在 -O2 下被完全内联,直接返回常量 42,零函数调用
+template <typename D> struct BenchBase {
+    int compute() { return static_cast<D*>(this)->compute_impl(); }
+};
+struct BenchConcrete : BenchBase<BenchConcrete> {
+    int compute_impl() { return 42; }
+};
+int use_crtp() {
+    BenchConcrete c;
+    return c.compute();
+}
+#endif
+
+int main() {
+    Circle c{2.0};
+    Square s{3.0};
+    std::cout << c.name() << " area = " << c.area() << "\n"; // Circle 走 Circle::area_impl
+    std::cout << s.name() << " area = " << s.area() << "\n"; // Square 走 Square::area_impl
+    return 0;
+}

code/examples/vol4/vol1-basics-cpp11-14/fixed_vector.cpp

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+// fixed_vector<T, N>:编译期定长、连续存储、零动态分配的 vector
+// 对应文章:documents/vol4-advanced/vol1-basics-cpp11-14/10-fixed-vector.md
+// 编译:g++ -Wall -Wextra -std=c++20 fixed_vector.cpp -o fixed_vector && ./fixed_vector
+#include <array>
+#include <cstddef>
+#include <iostream>
+#include <stdexcept>
+
+template <typename T, std::size_t N> class FixedVector {
+    std::array<T, N> data_{};
+    std::size_t size_ = 0;
+
+  public:
+    static constexpr std::size_t capacity_v = N;
+
+    constexpr void push_back(const T& value) {
+        if (size_ >= N)
+            throw std::out_of_range("FixedVector full");
+        data_[size_++] = value;
+    }
+    constexpr T& operator[](std::size_t i) { return data_[i]; }
+    constexpr const T& operator[](std::size_t i) const { return data_[i]; }
+    constexpr std::size_t size() const { return size_; }
+
+    // 裸指针当迭代器:元素连续存储,T* 天生满足随机访问迭代器要求
+    constexpr T* begin() { return data_.data(); }
+    constexpr T* end() { return data_.data() + size_; }
+    constexpr const T* begin() const { return data_.data(); }
+    constexpr const T* end() const { return data_.data() + size_; }
+};
+
+int main() {
+    FixedVector<int, 8> v;
+    for (int i = 1; i <= 5; ++i)
+        v.push_back(i * 10);
+
+    std::cout << "size = " << v.size() << " capacity = " << decltype(v)::capacity_v << "\n";
+    std::cout << "elements: ";
+    for (auto x : v)
+        std::cout << x << " ";
+    std::cout << "\n";
+    std::cout << "v[2] = " << v[2] << "\n";
+    std::cout << "sizeof(FixedVector<int,8>) = " << sizeof(FixedVector<int, 8>) << "\n";
+    std::cout << "sizeof(int*) = " << sizeof(int*) << " (动态 vector 至少含 3 个指针 + 堆分配)\n";
+    return 0;
+}

code/examples/vol4/vol1-basics-cpp11-14/type_traits_from_scratch.cpp

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+// 手写 type traits:主模板 + 偏特化,看穿 <type_traits> 的实现原理
+// 对应文章:documents/vol4-advanced/vol1-basics-cpp11-14/04-specialization-partial.md
+// 编译:g++ -Wall -Wextra -std=c++20 type_traits_from_scratch.cpp -o type_traits && ./type_traits
+#include <iostream>
+
+// is_pointer:主模板 false,指针偏特化 true
+template <typename T> struct is_pointer {
+    static constexpr bool value = false;
+};
+template <typename T> struct is_pointer<T*> {
+    static constexpr bool value = true;
+};
+
+// is_const:主模板 false,const T 偏特化 true(注意 const T* 不算,得 T 本身是 const)
+template <typename T> struct is_const {
+    static constexpr bool value = false;
+};
+template <typename T> struct is_const<const T> {
+    static constexpr bool value = true;
+};
+
+// is_reference:主模板 false,T& / T&& 偏特化 true
+template <typename T> struct is_reference {
+    static constexpr bool value = false;
+};
+template <typename T> struct is_reference<T&> {
+    static constexpr bool value = true;
+};
+template <typename T> struct is_reference<T&&> {
+    static constexpr bool value = true;
+};
+
+// C++14 变量模板简写(和标准库 _v 后缀同一思路)
+template <typename T> constexpr bool is_pointer_v = is_pointer<T>::value;
+
+int main() {
+    std::cout << std::boolalpha;
+    std::cout << "is_pointer<int>      = " << is_pointer<int>::value << "\n";
+    std::cout << "is_pointer<int*>     = " << is_pointer<int*>::value << "\n";
+    std::cout << "is_pointer<int**>    = " << is_pointer<int**>::value << "\n";
+    std::cout << "is_const<const int>  = " << is_const<const int>::value << "\n";
+    std::cout << "is_const<int>        = " << is_const<int>::value << "\n";
+    std::cout << "is_const<const int*> = " << is_const<const int*>::value
+              << " (指针自身非 const,指向 const)\n";
+    std::cout << "is_const<int* const> = " << is_const<int* const>::value << " (指针自身 const)\n";
+    std::cout << "is_reference<int&>   = " << is_reference<int&>::value << "\n";
+    std::cout << "is_reference<int&&>  = " << is_reference<int&&>::value << "\n";
+    std::cout << "is_pointer_v<double> = " << is_pointer_v<double> << " (_v 简写)\n";
+    return 0;
+}