C++ - 有没有办法为字段创建别名

Question

有没有办法为 C++11 中的类/结构创建别名？我的意思是

我上课了

class Vector4
{
    public:
        float X,Y,Z,W;
}

我有一个别名

typedef Vector4 Color;

有没有办法为 Vector4 X、Y、Z、W 字段创建别名以作为颜色 R、G、B、A 工作？

Answer 1

只需像这样定义 Vector4，使用匿名 union (没有匿名结构，尽管它们是常见的扩展)。

typedef struct Vector4
{
    union{float X; float R;};
    union{float Y; float G;};
    union{float Z; float B;};
    union{float W; float A;};
} Vector4;
typedef Vector4 Color;

如果您不能重新定义 Vector4，您可能只是定义一个布局兼容的标准布局类并使用可怕的 reinterpret_cast。
这是可行的，因为具有布局兼容成员的标准布局类是兼容的。

struct Color
{
    float R, G, B, A;
}

标准报价:

A standard-layout class is a class that:
— has no non-static data members of type non-standard-layout class (or array of such types) or reference,
— has no virtual functions (10.3) and no virtual base classes (10.1),
— has the same access control (Clause 11) for all non-static data members,
— has no non-standard-layout base classes,
— either has no non-static data members in the most derived class and at most one base class with non-static data members, or has no base classes with non-static data members, and
— has no base classes of the same type as the first non-static data member.

A standard-layout struct is a standard-layout class defined with the class-key struct or the class-key class.
A standard-layout union is a standard-layout class defined with the class-key union.