Re: union float[3] and x,y,z

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Tue, 25 Sep 2007 09:26:24 -0400
Message-ID:
<fdb2a0$ak7$1@news.datemas.de>
Erik Wikstr?m wrote:

On 2007-09-25 14:26, Gernot Frisch wrote:

Uhm...
Is there any way of making
float pos[3];
a union of
float x,y,z;

somehow, so I can use:

mything[0] = mything.y;
instead of mything.x = mything.y


No, however you can do something like this:

struct thing
{
 float arr[3];
 float& x;
 float& y;
 float& z;

 thing() : x(arr[0]), y(arr[1]), z(arr[2]) {}
};

Which allows you to access x through either t.x or through t.arr[0]
where t is an object of type thing:

int main()
{
thing t;
t.x = 1;
t.y = 2;
t.arr[2] = 3;

int i = 0;
}

If you want to be able to use t[0] instead of t.arr[0] you have to
overload the [] operator as Alexander Dong Back Kim suggested.


Actually, could still do that if you do this trick:

    struct thing {
        float x, y, z;
        struct thing_indexing {
            thing& t;
            thing_indexing(thing& t) : t(t) {}
            float& operator[](int i) {
                return i < 2 ? i < 1 ? t.x : t.y : t.z;
            }
        } arr;
        thing() : arr(*this) {}
        thing& operator=(thing const& t) {
            x = t.x;
            y = t.y;
            z = t.z;
        }
    };

    int main() {
        thing t;
        t.x = 3.1415926;
        t.arr[1] = t.x;
    }

RATS! I got pulled in and am writing code when I didn't want to....

V
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