Question

So I have this struct composed of three NSPoint structures.

typedef struct AOTriangle_ {
    NSPoint a;
    NSPoint b;
    NSPoint c;
} AOTriangle;

I would like in some cases to reference the points as a,b,c and other cases as indices into an array.

Like so,

AOTriangle t;
t.a = NSMakePoint(0,0);
t.b = NSMakePoint(3,0);
t.c = NSMakePoint(0,4);

for(int i = 0; i < 3; ++i) {
    t[i].x += 5.0;
    t[i].y += 5.0;
}

This is the closest I’ve gotten, but you can see it isn’t exactly what I wanted.
Is there a way of doing this in Objective-C? Is the a better way than what I do below of accomplishing something similar – maybe with a union?

typedef struct AOTriangle_ {
    NSPoint a;
    NSPoint b;
    NSPoint c;
} AOTriangle;


AOTriangle t;
t.a = NSMakePoint(0,0);
t.b = NSMakePoint(3,0);
t.c = NSMakePoint(0,4);
NSPoint* t = (NSPoint*)▵
for(int i = 0; i < 3; ++i) {
    t[i].x += 5.0;
    t[i].y += 5.0;
}

Answer 1

Yes, you can use a “union“. I believe the declaration would go something like this:

typedef struct AOTriangle_ {
    union {
        struct {
            NSPoint a;
            NSPoint b;
            NSPoint c;
        };
        NSPoint points[3];
    };
} AOTriangle;

A union is basically a way of saying “I can refer to the members of this struct as either a, b, or c, or as points[0], points[1], or points[2].”

And you would use it like this:

AOTriangle t;
t.a = NSMakePoint(0,0);
t.b = NSMakePoint(3,0);
t.c = NSMakePoint(0,4);
for(int i = 0; i < 3; ++i) {
    t.points[i].x += 5.0;
    t.points[i].y += 5.0;
}