struct Vector(int size, type) {
    union {
        struct {
            static if (size > 0) type x = 0;
            static if (size > 1) type y = 0;
            static if (size > 2) type z = 0;
            static if (size > 3) type w = 1;
        }
        // COMMENT this struct to fix the bug
        struct {
            static if (size > 0) type r;
            static if (size > 1) type g;
            static if (size > 2) type b;
            static if (size > 3) type a;
        }
    }
}

struct A {
    int n;
    Vector!(3, float) v;
}

void main() {
    Vector!(3, float) v;
    assert(v.x == 0, "v.x != 0");
    assert(v.y == 0, "v.y != 0");
    assert(v.z == 0, "v.z != 0");
    A a = A(); // OR simply use: A a;
    assert(a.v.x == 0, "a.v.x != 0");
    assert(a.v.y == 0, "a.v.y != 0");
    assert(a.v.z == 0, "a.v.z != 0");
}