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c++ - CRTP如何使派生类具有基类的容器

问题描述

我想使用 CRTP 模仿以下行为：

#include <vector>
#include <memory>

class GameNumber {
public:
    ~GameNumber(){}
};

class GameNumber_real : public GameNumber {
public:
    GameNumber_real (float m) {n = m;}
    ~GameNumber_real(){}
private:
    float n;
};

class GameNumber_sets : public GameNumber {
public:
    GameNumber_sets (float n, float m) {
        left.push_back (std::make_shared<GameNumber_real>
            (GameNumber_real(n)));
        right.push_back (std::make_shared<GameNumber_real>
            (GameNumber_real(m)));
    }
    ~GameNumber_sets(){}
private:
    std::vector <std::shared_ptr<GameNumber>> left;
    std::vector <std::shared_ptr<GameNumber>> right;
};

我的尝试是：

template <class T>
class GameNumber {}

class GameNumber_real : public GameNumber<GameNumber_real> {
public:
    GameNumber_real (float m) {n = m;}
private:
    float n;
};

class GameNumber_sets : public GameNumber<GameNumber_sets> {
public:
    GameNumber_sets (float n, float m) {
        left.push_back (std::make_shared<GameNumber_real>
            (GameNumber_real(n)));
        right.push_back (std::make_shared<GameNumber_real>
            (GameNumber_real(m)));
    }
private:
    std::vector <std::shared_ptr<GameNumber>> left;
    std::vector <std::shared_ptr<GameNumber>> right;
};

编译器错误是：

include/game_number.hpp:44:33: error: no matching function for call to
‘std::vector<std::shared_ptr<GameNumber<GameNumber_sets>>>
::push_back(std::shared_ptr<GameNumber_real>)’  
             (GameNumber_real(n)));

从消息中我了解到，在 GameNumber_sets 中，GameNumber 解析为 GameNumber_GameNumber_sets_。如果您能告诉我如何实现我所期望的行为，我将非常高兴。

标签： c++template-meta-programmingcrtp

解决方案

您可以显式指定模板参数GameNumber<GameNumber_real>，它将解决您的问题。

您也可以将构造函数参数直接传递给std::make_shared.

改进的代码：

template <class T>
class GameNumber {};

class GameNumber_real : public GameNumber<GameNumber_real> {
public:
    GameNumber_real (float m) {n = m;}
private:
    float n;
};

class GameNumber_sets : public GameNumber<GameNumber_sets> {
public:
    GameNumber_sets (float n, float m) {
        left.push_back (std::make_shared<GameNumber_real>(n));
        right.push_back (std::make_shared<GameNumber_real>(m));
    }
private:
    std::vector <std::shared_ptr<GameNumber<GameNumber_real>>> left;
    std::vector <std::shared_ptr<GameNumber<GameNumber_real>>> right;
};

但是我不明白为什么在这里需要 CRTP，在您的示例中没有使用它。

编辑：

据我所知，您不能使用 CRTP 作为接口。但是，如果 c++17 适合您，那么有std::any（https://en.cppreference.com/w/cpp/utility/any ）可能会有所帮助。

代码如下所示：

template <class T>
class GameNumber {};

class GameNumber_real : public GameNumber<GameNumber_real> {
public:
    GameNumber_real (float m) {n = m;}
private:
    float n;
};

class GameNumber_sets : public GameNumber<GameNumber_sets> {
public:
    GameNumber_sets (float n, float m) {
        left.push_back (std::make_shared<std::any>
            (GameNumber_real(n)));
        right.push_back (std::make_shared<std::any>
            (GameNumber_real(m)));
    }
private:
    std::vector <std::shared_ptr<std::any>> left;
    std::vector <std::shared_ptr<std::any>> right;
};

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