C ++实例化，在另一个类中，一个类型变量从一组具有相同构造函数的类 [英] C++ Instantiate, inside another class, a class-type variable from a group of classes with same constructor

问题描述

我在C ++中不高级。假设我有一组类，从 A 到任何（数字将随时间增长），使用相同类型的构造函数。假设它看起来像这样：

I am not advanced in C++. Suppose I have a group of classes, from A to whatever (the number will grow in time), that use the same type of constructor. Suppose it looks like this:

class A
{
private:
    double m_x, m_y;
public:
    A(const double &x, double &y, const short &n) { ... };
};

每个类都有相同的 m_x，m_y 变量，但它们的计算方式不同。现在有另一个类， Bla ，需要使用前一组类的构造函数，类似这样：

Each of these classes have the same m_x, m_y variables, but they calculate it differently. Now there's another class, say Bla, who needs to use the constructors from the previous group of classes, something like this:

class Bla
{
private:
    Class m_class;
public:
    Bla(const double &x, const double &y, const double &z, const short &i)
    {
        switch (i)
        {
        case 1: m_class = A::A(...); break;
        case 2: m_class = B::B(...); break;
        ...
        }
    }
};

在构造函数中的 switch（i）根据 i 选择组的构造函数之一。如何使类中的m_class 变量 Bla 与开关）在构造函数中？我应该选择什么类型的变量，或如何？

The switch (i) in the constructor chooses one of the group's constructor according to i. How can I make the Class m_class variable inside Bla to be consistent with the switch (i) in the constructor? What type of variable should I choose, or how?

或者， m_class 只需要保存 m_x，m_y 来自组中的一个类的变量，要进一步处理/计算/ etc，还有另一种方法吗？

Alternatively, m_class only needs to hold the m_x, m_y variables coming from one of the classes in the group, to be further processed/calculated/etc, is there another method of doing this? I hope I managed to be clear about this.

推荐答案

你可以有一个包含这些常用成员变量的接口类

You could have an interface class with those common member variables

class I
{
public:
    virtual ~I() = default;
protected:
    double m_x, m_y;
};

然后从中导出你的具体类，每个将填充 m_x 和 m_y 。

Then derive your concrete classes from that, each of which will populate m_x and m_y differently.

class A : public I
{
public:
    A(const double &x, double &y, const short &n) { ... };
};

然后你的 Bla 工厂并根据您的 i 参数取得特定类型的 I

Then your Bla constructor essentially acts as a factory and makes specific types of I depending on your i parameter

class Bla
{
private:
    std::unique_ptr<I> m_class;
public:
    Bla(const double &x, const double &y, const double &z, const short &i)
    {
        switch (i)
        {
        case 1: m_class = std::unique_ptr<I>(new A(...)); break;
        case 2: m_class = std::unique_ptr<I>(new B(...)); break;
        ...
        }
    }
};

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