Re: Implementing a smart pointer which works with incomplete types

Pete Becker wrote:


  Well, my tests with gcc disagree with this. That type of smart pointer
class correctly calls the destructor of the object, while a more
"traditional" doesn't.

  Getting the situation to happen is a bit complicated, but I have tried
to simplify it as much as possible:

//==================== GenericPtr.hh ====================
template<typename T>
class GenericPtr1 // "Traditional" smart pointer
{
    T* ptr;

 public:
    GenericPtr1(T* p): ptr(p) {}
    ~GenericPtr1() { delete ptr; }
};

template<typename T>
class GenericPtr2 // A version which should work with incomplete types
{
    T* ptr;
    typedef void(*DeleteFunctionType)(T* p);
    DeleteFunctionType deleteFunction;
    static void doDelete(T* p) { delete p; }

 public:
    GenericPtr2(T* p): ptr(p), deleteFunction(doDelete) {}
    ~GenericPtr2() { deleteFunction(ptr); }
};

//==================== AClass.hh ====================
#include "GenericPtr.hh"

class ClassToBeManaged;

class AClass
{
    GenericPtr1<ClassToBeManaged> ptr1;
    GenericPtr2<ClassToBeManaged> ptr2;

 public:
    AClass();
};

//==================== AClass.cc ====================
#include "AClass.hh"
#include "ClassToBeManaged.hh"

AClass::AClass():
    ptr1(new ClassToBeManaged(1)), ptr2(new ClassToBeManaged(2))
{}

//==================== ClassToBeManaged.hh ====================
class ClassToBeManaged
{
    int id;

 public:
    ClassToBeManaged(int i);
    ~ClassToBeManaged();
};

//==================== ClassToBeManaged.cc ====================
#include "ClassToBeManaged.hh"
#include <iostream>

ClassToBeManaged::ClassToBeManaged(int i): id(i)
{ std::cout << "Constructed " << id << std::endl; }

ClassToBeManaged::~ClassToBeManaged()
{ std::cout << "Destructed " << id << std::endl; }

//==================== test.cc ====================
#include "AClass.hh"

int main()
{
    AClass a;
}

  Running this program produces:

Constructed 1
Constructed 2
Destructed 2

  This means that GenericPtr1 did not call the destructor of
ClassToBeManaged properly, while GenericPtr2 did.