Pimpl idiom

[Peter Kümmel]

Marc Mutz wrote:
>> It is pure C++ and needs no macros or static variables.
> 
> Yes, and since it uses no macros, it doesn't support the
>   Derived::Private : public Base::Private
> optimization found in Qt4... 

I've written a small test program
to see the problem you are talking about:


#include "KImpl.h"
#include <iostream>

namespace Private
{
    int count = 1;

    struct BImpl
    {
        BImpl()
        {
            std::cout << "BImpl created, " <<count<< "\n";
            count++;
        }
        void foo(){std::cout<<"BImpl::foo()\n";}
    };

    struct CImpl : BImpl
    {
        CImpl() : BImpl()
        {
            std::cout<<"CImpl created \n";
        }
        void foo(){std::cout<<"CImpl::foo()\n";}
    };
}


struct B
{
    B()
    {
        d->foo();
    }
    KPimpl<Private::BImpl> d;
};


struct C : B
{
    C() : B()
    {
        d->foo();
    }
    KPimpl<Private::CImpl> d;
};

int main()
{
    C c;
    system("pause");
    return 0;
}


And the output is:

BImpl created, 1
BImpl::foo()
BImpl created, 2
CImpl created
CImpl::foo()


The "only" problem I see is the multiple creation of BImpl,
am I right?
Or are there more problems?

Maybe there is a macro-free way to handle this problem.

Peter