c++ - 如何使用点运算符在 C++ 中定义嵌套函数？

Question

我想用点运算符创建函数，如下所示：

Regedit.Key.Create();
Regedit.Value.Create();
Regedit.Value.Read();

我怎样才能做到这一点？

Answer 1

在 C++ 中，您需要编写 getter 函数，然后语法变为 editor.Key().Create();

class Key
{
public:
    Key() = default;
    ~Key() = default;

    void Create() 
    {
    };
};

class RegEdit
{
public:
    // in C++ you need to use a getter function 
    Key& key() 
    {
        return m_key;
    }

private:
    Key m_key;
};

int main()
{
    RegEdit editor;
    editor.key().Create();

    return 0;
}

Answer 2

要Regedit.Key.Create();成为有效的 C++ 指令，需要一些条件：

• Regedit必须是对象（即 C++ 类的实例）
• Key必须是的成员属性Regedit
• 该属性也必须是一个对象
• Create必须是该对象的方法

这是一个满足这些条件的示例代码，其中RegAccessor的类是Regedit和Selector的类Regedit.Key：

#include <iostream>

class Selector {
public:
    enum class Type {
        Key,
        Value
    };
    friend std::ostream& operator << (std::ostream& out, const Type& type) {
        const char *name;
        switch (type) {
            case Type::Key: name = "Key"; break;
            case Type::Value: name="Value"; break;
            default: name="Unknown";
        }
        out << name;
        return out;
    }
    
    Selector(Type type): type(type) {};
    
    void Create() {
        // write more relevant code here...
        std::cout << "Create " << type << " called\n";
    }
    void Read() {
         // write more relevant code here...
       std::cout << "Read " << type << " called\n";
    }

private:
    Type type;
};



class RegAccessor {
public:
    Selector Key = Selector::Type::Key;
    Selector Value = Selector::Type::Value;
};

int main(int argc, char **argv)
{
    RegAccessor Regedit;
    // here is exactly your example code
    Regedit.Key.Create();
    Regedit.Value.Create();
    Regedit.Value.Read();
    return 0;
}