fatptr.cc

#include <format>
#include <print>
#include <string>
#include <vector>

struct Dog {
    std::string name;
    void Say() const {
        std::print("{}: Woof!\n", name);
    }
};

struct Cat {
    std::string name;
    void Say() const {
        std::print("{}: Meow!\n", name);
    }
};

struct MemberSayDecl {
    void Say() const;
};

struct MemberSayImpl {
    void* value;
    void (*SayImpl)(void*);
    void Say() const {
        SayImpl(value);
    }
};

struct MemberSayFatPtr {
    template<typename T>
    MemberSayFatPtr(T* v) :
        impl{
            reinterpret_cast<void*>(v),
            [](void* self) {
                auto obj = static_cast<T*>(self);
                obj->Say();
            },
        } { }

    MemberSayImpl* operator->() {
        return &impl;
    }
    MemberSayImpl operator*() {
        return impl;
    }

  private:
    MemberSayImpl impl;
};

int main() {
    auto c = Cat("a");
    auto d = Dog("d");

    auto p = std::vector<MemberSayFatPtr>{&c, &d};
    p[0]->Say();
    p[1]->Say();
}

问题：

1、c++26不支持编译期动态类型，只支持编译期动态结构体，GG。。。
2、const的member function需要区分