联盟需要破解 [英] Union hack needed

问题描述

我有一个结构的重新presents一个顶点。它具有的x，y和z领域以及其他几个人。最近，我来到结论，对于某些功能，我将需要访问的顶点坐标的数组。我不想污染的code。与临时变量或更改像这样所有地方 VY 这个 v.coord [1] 这是不是很好也不优雅。所以我想过使用工会。像这样的东西应该工作：

I have a struct that represents a vertex. It has x, y and z fields as well as several others. Recently I came into conclusion that for certain functionality I will need to access the coordinates of the vertex as an array. I didn't want to "pollute" the code with temporary variables or change all places that look like this v.y to this v.coord[1] which is not nice nor elegant. So I thought about using a union. Something like this should work:

struct {
  float x,y,z;
} Point;

struct {
    union {
        float coord[3];
        Point p;
    };
} Vertex;

这是不错的，但并不完美。点类没有点在那里。我希望能够访问只需键入 V.Y （而不是 v.p.y ），y坐标。结果
你可以建议一个黑客来解决这个（或告诉我，这是不可能的）？

This is good, but not perfect. The point class has no point being there. I want to be able to access y coordinate simply by typing v.y (and not v.p.y).
Can you suggest a hack to solve this (or tell me that it is not possible)?

推荐答案

一个很好的C ++的方法是使用一个名为访问返回引用的元素：

A good C++ approach is to use named accessors that return references to the elements:

class Point {
public:
    float& operator[](int x)       { assert(x <= 2); return coords_[x]; }
    float  operator[](int x) const { assert(x <= 2); return coords_[x]; }

    float& X()       { return coords_[0]; }
    float  X() const { return coords_[0]; }

    float& Y()       { return coords_[1]; }
    float  Y() const { return coords_[1]; }

    float& Z()       { return coords_[2]; }
    float  Z() const { return coords_[2]; }
private:
    float coords_[3];
};

通过这种方式，给定一个 P点; ，您可以同时使用 P [0] 和的pX（）来访问内部 COORDS的初始元素_ 阵列。

With this approach, given a Point p;, you can use both p[0] and p.X() to access the initial element of the internal coords_ array.

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