The problem

Following Exercise #10: Obtaining a read-only (smart?) pointer a programmer has written the following class:


#include <boost/checked_delete.hpp>



struct MyStruct

{

  int m_x;



  private:

  ~MyStruct() {}

  friend void boost::checked_delete<>(MyStruct *);

};

Writing such a class enables safe forward declarations and forces the user of this class to use smart pointers, which is a good thing [1].

This programmer wants to use a class managing a std::vector of boost::shared_ptr of MyStruct, but he/she also wants to let the user obtain a std::vector of read-only smart pointers/pointers, that can be copied freely.

The code below shows the choices and some lines that should and should not compile:


#include <vector>

#include <boost/checked_delete.hpp>

#include <boost/shared_ptr.hpp>



struct MyStruct

{

  int m_x;



  private:

  ~MyStruct() {}

  friend void boost::checked_delete<>(MyStruct *);

};



struct MyStructKeeper

{

  std::vector</* ??? */> Get() const { /* ??? */ }

  private:

  std::vector<boost::shared_ptr<MyStruct> > m_v;

};



int main()

{

  MyStructKeeper k1;

  MyStructKeeper k2;

  std::vector</* ??? */> v1 = k1.Get();

  const std::vector</* ??? */> v2 = k2.Get();

  std::copy(v2.begin(),v2.end(),std::back_inserter(v1));

  v1[0]->m_x = 0; //Should not compile

  delete v1[0].get(); //Should not compile

}

What should the question marks be?

View the answer of this part of the exercise

References

Herb Sutter, Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. 2005. ISBN: 0-32-111358-6. Chapter 13: 'Ensure resources are owned by objects. Use explicit RAII and smart pointers.

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.

(C++) Exercise #11: Obtaining a std::vector of read-only (smart?) pointers

The problem

References