questions about @intToEnum

wnd_proc.zig

fn main_wnd_proc(hwnd: user32.HWND, u_msg: std.os.windows.UINT,
                 wParam: std.os.windows.WPARAM, lParam: std.os.windows.LPARAM)
                 callconv(.Stdcall) std.os.windows.LRESULT {
//   print_win32_message(u_msg);
  var result: windows.LRESULT = null;
  switch (@intToEnum(u_msgs, u_msg)) {
    u_msgs.WM_DWMNCRENDERINGCHANGED => {
      return user32.DefWindowProcA(hwnd, u_msg, wParam, lParam);
    },
    u_msgs.WM_ERASEBKGND  => {
      return user32.DefWindowProcA(hwnd, u_msg, wParam, lParam);
    },
    u_msgs.WM_NCLBUTTONDOWN  => {
      return user32.DefWindowProcA(hwnd, u_msg, wParam, lParam);
    },
    u_msgs.WM_CLOSE => run = false,
    else => {
      return user32.DefWindowProcA(hwnd, u_msg, wParam, lParam);
    }
  }
  std.debug.print("\n", .{});
  return result;
}