Refactor modern rectangle example

Author: XuhuaHuang

FriendClass/modern_square_rectangle.cpp

@@ -0,0 +1,66 @@
+/**
+ * @file modern_square_rectangle.cpp
+ * @author Xuhua Huang
+ * @brief
+ * @version 0.1
+ * @date 2026-04-04
+ *
+ * @copyright Copyright (c) 2026
+ *
+ */
+
+#include <iostream>
+
+class rectangle_t {
+private:
+  int width{0};
+  int height{0};
+
+public:
+  constexpr inline rectangle_t() = default;
+
+  constexpr inline rectangle_t(int w, int h)
+    : width(w)
+    , height(h) {}
+
+  void set_width(int w) noexcept { width = w; }
+  void set_height(int h) noexcept { height = h; }
+
+  [[nodiscard]]
+  int get_width() const noexcept {
+    return width;
+  }
+
+  [[nodiscard]]
+  int get_height() const noexcept {
+    return height;
+  }
+
+  [[nodiscard]]
+  int area() const noexcept {
+    return width * height;
+  }
+
+  // Preferred: member function instead of friend
+  [[nodiscard]]
+  rectangle_t double_in_size() const noexcept {
+    return rectangle_t(width * 2, height * 2);
+  }
+};
+
+// Optional: keep a free function wrapper if needed
+[[nodiscard]]
+rectangle_t double_in_size(const rectangle_t& rect) noexcept {
+  return rect.double_in_size();
+}
+
+int main() {
+  rectangle_t r1;
+  rectangle_t r2(2, 3);
+
+  r1 = double_in_size(r2);
+
+  std::cout << r1.area() << std::endl;
+
+  return 0;
+}