Four Questions on boost::shared_ptr

4 Feb 2002

      Hi,

I've got several questions about the former version of boost::shared_ptr. Would someone please help me?

1. Mr Stroustrup said that there wasn't a need for auto_array, for "a better solution is to use a vector". So, should we use vector or scoped_array/shared_array?

2. In the document, four implementations are said to have been discussed: Direct detached, Indirect detached, Embedded detached and Placement detached. I've tried to describle them (Are I right? See the attached file), but I don't understand the Placement detached. Could someone please tell me what it's like?

3. In the file smart_ptr.hpp, we can see the private function shared_ptr::share.
   void share(T* rpx, long* rpn) {
      if (pn != rpn) { 
         ++*rpn; // done before dispose() in case rpn transitively
                 // dependent on *this (bug reported by Ken Johnson)
         dispose();
         px = rpx;
         pn = rpn;
      }
   } // share
I'm sorry that I don't understand that reason why ++*rpn should be done before dispose(). Would someone please give me an example? Or is it like this?
  #include <boost/smart_ptr.hpp>
  struct A
  {
    boost::shared_ptr<A> v;
  };
  int main()
  {
    A* pa = new A;
    boost::shared_ptr<A> ptr(pa);
    ptr = pa->v;
  }

4. Why not use policies? I'm afraid that the word "parameterization will discourage users" might not be always true, for we can use default parameters.

Jon Wang
2002-01-31