Re: Re: shared_ptr swap problems

From: Olaf Petzold (yg-boost-users_at_[hidden])
Date: 2002-08-27 08:57:27

Thanks for answers,

the const ptr was a fault.

Well, the following example shows the problem in detail:

----8<----
#include <iostream>
#include <boost/shared_ptr.hpp>

struct Spec {
  Spec(const char* n) : m_name(n) { }
  void member() const { std::cout << "Hold " << m_name << std::endl; }
  const char*                           m_name;
};

struct SpecLP : public Spec {
  SpecLP(const char* n) : Spec(n) {  std::cout << "construct " << m_name << 
std::endl; }
  ~SpecLP() {  std::cout << "destruct  " << m_name << std::endl; }
};

struct SpecHP : public Spec {
  SpecHP(const char* n) : Spec(n) {  std::cout << "construct " << m_name << 
std::endl; }
  ~SpecHP() {  std::cout << "destruct  " << m_name << std::endl; }
};

struct Doc {
  virtual ~Doc() { }
  virtual void set(boost::shared_ptr<Spec>& ptr) = 0;
};

struct LpDoc : public Doc {
  LpDoc() : m_lp( new SpecLP("LpDoc::lp") ) { }
  void set(boost::shared_ptr<Spec>& spec) {
    // m_lp = boost::shared_static_cast<SpecLP>( spec );
    m_lp = boost::shared_polymorphic_cast<SpecLP>( spec );
  }
  void print() { m_lp->member(); }
  boost::shared_ptr<SpecLP>             m_lp;
};

struct HpDoc : public Doc {
  HpDoc() : m_hp( new SpecHP("HpDoc::hp") ) { }
  void set(boost::shared_ptr<Spec>& spec) {
    // m_hp = boost::shared_static_cast<SpecHP>( spec );
    m_hp = boost::shared_polymorphic_cast<SpecHP>( spec );
  }
  void print() { m_hp->member(); }
  boost::shared_ptr<SpecHP>             m_hp;
};

int main()
{
  boost::shared_ptr<Spec> lp( new SpecLP("lp") );
  boost::shared_ptr<Spec> hp( new SpecHP("hp") );
  LpDoc doc;

  std::cout << "Case 1:\n";
  doc.print();
  doc.set( lp );        // is O.K.
  doc.print();

  std::cout << "Case 2:\n";
  try {
    doc.print();
    doc.set( hp );      // should throw
    doc.print();
  }
  catch(const std::bad_alloc& e) {
    std::cerr << "Exception \"" << e.what() << "\" catched\n";
  }
}

---->8----

It doesn't compile with shared_ptr. Imho is the polymorph code correct 
expect the pointer problem.

Thanks
Olaf