通用C ++類的非侵入式設計

Question

我正在嘗試使用C ++ 14，模板和Bridge模式，創建一種將對象添加到名為Shapes（Shape對象的矢量）的容器的通用方法。 我希望能夠自動支持添加到容器中的新數據類型並打印它們，而無需修改Shape類的原始實現。 相反，我只想提供一個新的print（T）函數，並且所有內容都可以直接使用。

以下是我的代碼，在編譯時仍然存在一些問題。 有人可以幫我嗎？ 非常感謝。

#include <iostream>
#include <memory>
#include <vector>
#include <map>
#include <string>

using namespace std;

void print(const int toPrint) {
    cout << " " << toPrint;
    cout << endl;
}

void print(const double toPrint) {
    cout << " " << toPrint;
    cout << endl;
}

void print(const vector<int> & toPrint) {
    for (auto & it : toPrint) {
        cout << " " << it;
    }
    cout << endl;
}

void print(const map<int, string> & toPrint) {
    for (auto & it : toPrint) {
        cout << "     " << it.first << " : " << it.second << endl;
    }
    cout << endl;
}

class Shape {
public:
    template<typename T>
    Shape(T &&t) {
        pimpl_ = make_unique<Specialization<T>>(t);
    }
    void print() const {
        pimpl_->print();
    }
private:
    struct Base {
        virtual void print() const = 0;
        virtual ~Base() = default;
    };

    template<typename T>
    struct Specialization: public Base {
        Specialization(T &t) :
                internalObject_ { std::move(t) } {
        }
        void print() const override {
            ::print(internalObject_);
        }

        T internalObject_;
    };

    unique_ptr<Base> pimpl_; 

};

typedef vector<Shape> Shapes;

void print(Shapes const & shapes) {
    for (auto & shape : shapes) {
        shape.print();
    }
}

int main() {
    Shapes shapes;

    shapes.push_back(1);
    shapes.push_back(2.0);
    shapes.push_back(0.3);

    shapes.push_back(vector<int> { 10, 11, 12 });
    shapes.push_back(map<int, string> { { 0, "elmo" }, { 1, "leom" } });

    print(shapes);
    return 0;
}

Answer 1

這是您的代碼的修補版本（使用clang編譯）。 正如評論中指出的那樣， 有幾個問題需要解決 （例如，此代碼泄漏內存），但這應該可以使您回到正軌。

#include <iostream>
#include <vector>

using namespace std;

void print(int toPrint) {
    cout << " " << toPrint;
    cout << endl;
}

void print(double toPrint) {
    cout << " " << toPrint;
    cout << endl;
}

void print(vector<int> toPrint) {
    for (auto & it : toPrint) {
        cout << " " << it;
    }
    cout << endl;
}

class Shape {
public:
    template<typename T>
    Shape(T t) {
        pimpl_ = new Specialization<T>(t);
    }
    void print() const{
        pimpl_->print();
    }
private:
    struct Base {
        virtual void print() const = 0;
    };

    template<typename T>
    struct Specialization: public Base {
        Specialization(T t) {
            internalObject_ = new T(t);
        }
        void print() const{
            ::print(*internalObject_);
        }

        T* internalObject_;
    };

    Base * pimpl_;
};

typedef vector<Shape> Shapes;

void print(Shapes const & shapes) {
    for (auto & shape : shapes) {
        shape.print();
    }
}

int main() {
    Shapes shapes;

    shapes.push_back(1);
    shapes.push_back(2.0);
    shapes.push_back(0.3);

    shapes.push_back(vector<int> { 10, 11, 12 });
    print(shapes);
    return 0;
}