在两个以上类的对象之间重载operator = [英] Overloading operator= between objects of more than two classes

问题描述

我为我的应用程序定义了三个类： int2 _ （整数对）， float2 _ 浮动）和 double2 _ （双双），主要用于执行复杂的算术运算。

I'm defining three classes for my application: int2_ (couples of integers), float2_ (couples of floats) and double2_ (couples of doubles), essentially to perform complex arithmetics operations.

我想重载上述三个类的对象之间的赋值 = 运算符。动机是我编写一个CUDA代码，但似乎没有为CUDA类定义的赋值运算符 int2 ， float2 和 double2 。

I want to overload the assignment = operator between objects of the above three classes. The motivation is that I'm writing a CUDA code, but it seems that there is no assignment operator already defined for the CUDA classes int2, float2 and double2.

我目前的实作方式如下：

My current implementation is the following:

class int2_ {

    public:
        int x;
        int y;

        int2_() : x(), y() {}

        // Stuff
        const int2_& operator=(const float2_ a)     { int2_ b;  b.x = (int)a.x;             b.y = (int)a.y;     return b; }
        const int2_& operator=(const double2_ a)    { int2_ b;  b.x = (int)a.x;             b.y = (int)a.y;     return b; }
};

class float2_ {

    public:
        float x;
        float y;

        float2_() : x(), y() {}

        // Stuff
        const float2_& operator=(const double2_ a)  { float2_ b;    b.x = (float)a.x;       b.y = (float)a.y;   return b; }
};

class double2_ {

    public:
        double x;
        double y;

        double2_() : x(), y() {}

        // Stuff
};

一切都被归纳为 stuff 不提供编译错误。剩余的操作符重载返回以下错误：

Everything is summarized as stuff does not provide compilation errors. The remaining operator overloads return the following errors

error : identifier "float2_" is undefined
error : identifier "double2_" is undefined  
error : identifier "double2_" is undefined  

分别为三个不同的重载。

respectively for the three different overloads.

似乎存在一个可见性问题，因为例如 float2 _ 在 int2 _ 类定义之前尚未定义code> double2 _ 。任何建议如何解决问题？非常感谢。

It seems that there is a "visibility" problem due to the fact that, for example, float2_ and double2_ are not yet defined before the int2_ class definition. Any suggestion on how solving the problem? Thank you very much in advance.

解决方案按照JAMES KANZE和ALEXRIDER的答案

这里是解决方案：

class int2_;
class float2_;
class double2_;

class int2_ {

    public:
        int x;
        int y;

        int2_() : x(), y() {}

        inline const int2_& operator=(const int a)          { x = a;            y = 0.;         return *this; }
        inline const int2_& operator=(const float a)        { x = (int)a;       y = 0.;         return *this; }
        inline const int2_& operator=(const double a)       { x = (int)a;       y = 0.;         return *this; }
        inline const int2_& operator=(const int2_ a)        { x = a.x;          y = a.y;        return *this; }
        inline const int2_& operator=(const float2_ a);
        inline const int2_& operator=(const double2_ a);
};

class float2_ {

    public:
        float x;
        float y;

        float2_() : x(), y() {}

        inline const float2_& operator=(const int a)        { x = (float)a;     y = 0.;         return *this; }
        inline const float2_& operator=(const float a)      { x = a;            y = 0.;         return *this; }
        inline const float2_& operator=(const double a) { x = (float)a;     y = 0.;         return *this; }
        inline const float2_& operator=(const int2_ a)      { x = (float)a.x;   y = (float)a.y; return *this; }
        inline const float2_& operator=(const float2_ a)    { x = a.x;          y = a.y;        return *this; }
        inline const float2_& operator=(const double2_ a);
};

class double2_ {

    public:
        double x;
        double y;

        double2_() : x(), y() {}

        inline const double2_& operator=(const int a)       { x = (double)a;    y = 0.;         return *this; }
        inline const double2_& operator=(const float a) { x = (double)a;    y = 0.;         return *this; }
        inline const double2_& operator=(const double a)    { x = a;            y = 0.;         return *this; }
        inline const double2_& operator=(const int2_ a) { x = (double)a.x;  y = (double)a.y;return *this; }
        inline const double2_& operator=(const float2_ a)   { x = (double)a.x;  y = (double)a.y;return *this; }
        inline const double2_& operator=(const double2_ a)  { x = a.x;          y = a.y;        return *this; }

};

        inline const int2_& int2_::operator=(const float2_ a)       { x = (int)a.x;             y = (int)a.y;       return *this; }
        inline const int2_& int2_::operator=(const double2_ a)      { x = (int)a.x;             y = (int)a.y;       return *this; }
        inline const float2_& float2_::operator=(const double2_ a)  { x = (float)a.x;           y = (float)a.y;     return *this; }

推荐答案

首先，类：

class Int2;
class Float2;
class Double2;

。实现应该在所有的
类定义之后，或者在单独的源文件中，或者
显式声明为inline。

Then, in the classes, you should only declare the functions, not implement them. The implementations should come after all of the class definitions, either in a separate source file, or explicitly declared inline.

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