title: why view.center is assignable but view.frame.origin or view.frame.size are not
body: <p>[sorry for my weak english]</p>
  
  <p>question as stated in the title:</p>
  
  <p>why view.center is assignable but view.frame.origin 
  or view.frame.size are not :-!</p>
  
  <p>it is not undesterable by me</p>