C++ Templates 模版

还在装修中
- Curiously Recurring Template Pattern (CRTP)
花絮
参考资料

还在装修中

Under constructions…..

(因为我还没有能力理解 C++ 模版)

Curiously Recurring Template Pattern (CRTP)

这东东在 LLVM New Pass Manager 用了。詹哥也说了，学这些高级概念需要结合项目。可以在

例如去参加 2022年的 OceanBase 数据库大赛 或者阅读 LLVM 源码。

C++ Templates - Part 4 : Curiously Recurring Template Pattern

这个理论好像是偶然发现的 (有点神奇，CS 竟然不是像那种业务是故意设计出来的)。

目的都是 Reuse of Code,

下面的例子是 Python 或者 Java 的 Deep Clone 的样例

#include <vector>
#include <iostream>

struct Shape{
    virtual ~Shape() = default;

    template <typename T> 
    T* Clone() {return new T(); }
};

struct Square : public Shape{
    int x = 1; 
};

struct Rectangle : public Shape{
    int x = 1, y = 1; 
}; 


int main(){
    std::vector<Shape*> v; 
    v.push_back(new Square()); 
    v.push_back(new Rectangle()); 

    for (int i = 0; i < 2; i++){
        Shape *s = v[i]; 
        Shape *c = nullptr; 
        if (Square *ds = dynamic_cast<Square*>(s)){
            c = s->Clone<Square>(); 
        }else if (Rectangle *ds = dynamic_cast<Rectangle*>(s)){
            c = s->Clone<Rectangle>(); 
        }
    }

    return 0; 
}

但是使用 CRTP 的概念后 (使用 Template 辅助传递信息)

struct Shape{
    virtual Shape* Clone() = 0; 
    virtual ~Shape() = default;
    virtual void print() = 0; 
};

template <typename T> 
struct ShapeCRTP : public Shape{ 
    virtual Shape* Clone() override { 
        return new T(*static_cast<T*>(this)); 
    }
}; 

struct Square : public ShapeCRTP<Square>{
    int x = 1; 
    virtual void print() override{
        std::cout << "Square: (" << x << ")\n";  
    }
};

struct Rectangle : public ShapeCRTP<Rectangle>{
    int x = 1, y = 1; 
    virtual void print() override{  
        std::cout << "Rectangle: (" << x << ", " << y << ")\n";  
    }   
}; 


int main(){
    std::vector<Shape*> v; 
    v.push_back(new Square); 
    v.push_back(new Rectangle); 
    for (int i = 0; i < 2; i++){
        Shape *c = v[i]->Clone(); 
        c->print(); 
    }
    return 0; 
}

还在装修中

Curiously Recurring Template Pattern (CRTP)

花絮

参考资料