title: assign value of readonly variable in private method called only by constructors
body: <p>C# compiler gave me the following error</p>
  
  <p>CS0191: A readonly field cannot be assigned to (except in a constructor or a variable initializer)</p>
  
  <p>Do I have to move the code (in my private function) into the constructor? That sounds awkward. </p>
  
  <p>Note that the private method was intended only to be called by the constructor. I expect that there is some sort of attribute that I can use to mark the method corresponding.</p>