diff --git a/include/line.hpp b/include/line.hpp
index 6819ead..357b51a 100644
--- a/include/line.hpp
+++ b/include/line.hpp
@@ -93,6 +93,8 @@ public:
             circularArcs[i].h = ABHalf.norm() * std::tan(theta * 0.5);
             circularArcs[i].center = A + ABHalf + QONorm * circularArcs[i].h;
             circularArcs[i].theta = theta;
+            Vec3 a;
+            a = ABHalf.cross(QONorm);
             circularArcs[i].radius = (circularArcs[i].center - A).norm();
             circularArcs[i].u = (A - circularArcs[i].center).normalize();
             circularArcs[i].v = ABNorm.cross(circularArcs[i].u);
@@ -192,7 +194,7 @@ public:
         else printf("Open Polyline: \n");
         printf("Points: {\n");
         for (int i = 0; i < _points.size(); ++i) {
-            printf("<%lf, %lf, %lf>", _points[i].x, _points[i].y, _points[i].z);
+            printf("<%lf, %lf, %lf>", _points[i].x(), _points[i].y(), _points[i].z());
             if (i != _points.size() - 1) printf(", ");
         }
         std::cout << "}" << std::endl;
diff --git a/include/solid.hpp b/include/solid.hpp
index e586614..460f03a 100644
--- a/include/solid.hpp
+++ b/include/solid.hpp
@@ -44,7 +44,7 @@ public:
             auto uv = get2DRepOf3DPt(QP, N, B, Q);
             // test it
             {}
-            _localProfile2D.emplace_back(uv.x, uv.y);
+            _localProfile2D.emplace_back(uv.x(), uv.y());
         }
     }
 
@@ -59,7 +59,7 @@ public:
         Vec3 QP = p - Q;
         auto uv = get2DRepOf3DPt(QP, N, B, Q);
         // test it
-        {}
+        // TODO: to test if uv is in _localProfile2D
         return 0;
     }
 };
diff --git a/include/vec.hpp b/include/vec.hpp
index a50ae7c..b10d6c6 100644
--- a/include/vec.hpp
+++ b/include/vec.hpp
@@ -24,13 +24,12 @@ public:
         static_assert(sizeof...(args) == N, "Argument count must match vector size.");
     }
 
-    explicit VecBase(const Derived &v) {
+    explicit VecBase(const VecBase &v) {
         data = v.data;
     }
 
-    VecBase& operator=(const VecBase &v) {
-        if (this == &v) return *this;
-        data = v.data;
+    VecBase &operator=(VecBase v) {
+        *this = std::move(v);
         return *this;
     }
 
@@ -106,53 +105,61 @@ public:
     }
 };
 
-
 // Vec<2> 特化
 class Vec2 : public VecBase<Vec2, 2> {
 public:
-    union {
-        struct {
-            real &x, &y;
-        };
-        struct {
-            real &u, &v;
-        };
-        struct {
-            real &a, &b;
-        };
-    };
-
-    Vec2(real xVal, real yVal) : VecBase<Vec2, 2>(xVal, yVal), x(data[0]), y(data[1]) {}
-
-    Vec2() : VecBase<Vec2, 2>(), x(data[0]), y(data[1]) {}
-
-    Vec2(const Vec2 &v) : VecBase<Vec2, 2>(v), x(data[0]), y(data[1]) {}
+    Vec2() : VecBase() {}
+    Vec2(real x, real y) : VecBase(x, y) {}
+    Vec2(const Vec2& v) : VecBase(v.x(), v.y()) {}
+
+    Vec2 &operator=(const Vec2& v) {
+        data = v.data;
+        return *this;
+    }
+
+    real& x() { return data[0]; }
+    real& y() { return data[1]; }
+
+    const real& x() const { return data[0]; }
+    const real& y() const { return data[1]; }
+
+    real& u() { return data[0]; }
+    real& v() { return data[1]; }
+
+    const real& u() const { return data[0]; }
+    const real& v() const { return data[1]; }
 };
 
 
-// specialize template class Vec<3>;
 class Vec3 : public VecBase<Vec3, 3> {
 public:
-    union {
-        struct {
-            real &x, &y, &z;
-        };
-        struct {
-            real &u, &v, &w;
-        };
-        struct {
-            real &a, &b, &c;
-        };
-    };
-
-    Vec3() : VecBase<Vec3, 3>(), x(data[0]), y(data[1]), z(data[2]) {}
-
-    Vec3(real xVal, real yVal, real zVal) : VecBase<Vec3, 3>(xVal, yVal, zVal), x(data[0]), y(data[1]), z(data[2]) {}
-
-    Vec3(const Vec3 &vec) : VecBase<Vec3, 3>(vec), x(data[0]), y(data[1]), z(data[2]) {}
-
-    Vec3 cross(const Vec3 &v) const {
-        return {y * v.z - z * v.y, z * v.x - x * v.z, x * v.y - y * v.x};
+    Vec3() : VecBase() {}
+    Vec3(real x, real y, real z) : VecBase(x, y, z) {}
+    Vec3(const Vec3& v) : VecBase(v.x(), v.y(), v.z()) {}
+
+    Vec3 &operator=(const Vec3& v) {
+        data = v.data;
+        return *this;
+    }
+
+    real& x() { return data[0]; }
+    real& y() { return data[1]; }
+    real& z() { return data[2]; }
+
+    real x() const { return data[0]; }
+    real y() const { return data[1]; }
+    real z() const { return data[2]; }
+
+    real& u() { return data[0]; }
+    real& v() { return data[1]; }
+    real& w() { return data[2]; }
+
+    real u() const { return data[0]; }
+    real v() const { return data[1]; }
+    real w() const { return data[2]; }
+
+    Vec3 cross(const Vec3& v) const {
+        return {y() * v.z() - z() * v.y(), z() * v.x() - x() * v.z(), x() * v.y() - y() * v.x()};
     }
 };