Re: [boost] Shared pointers and pointers to members issue (with fix)

From: Michael Marcin (mmarcin_at_[hidden])
Date: 2007-03-01 12:41:42

Michael Anderson wrote:
> <snip>
>
> For example I want this to work... where ptr<Bar> is some kind of
> smart (or otherwise) pointer to a bar object.
>
> {
>   ptr<Bar> barPtr;
>   {
>     ptr<Foo> fooPtr(new Foo);
>     barPtr = fooPtr->bar;
>     //A
>   }
>   barPtr->doSomething(); //B
>   //C
> }
>
> Note that fooPtr goes out of scope at line A, but if the Foo object is
> destroyed at A then line B is an error. Instead I want the Foo object
> to exist until line C where both barPtr and fooPtr go out of scope.
>
> <snip>
>

I see...

This sort of usage smells bad to me but if you have solid reasons behind it 
perhaps this is a case for 2 shared pointers using the same reference count 
object as was discussed on this list a while ago.

i.e. something like

class Bar {};
class Foo : enable_shared_from_this<Foo>
{
public:
    Foo() : bar( shared_ptr<Bar>(new Bar, shared_from_this()) ) {}
    weak_ptr<Bar> bar;
};

{
    shared_ptr<Bar> barPtr;
   {
     shared_ptr<Foo> fooPtr(new Foo);
     barPtr = fooPtr->bar.lock();
   }      //A
   barPtr->doSomething();
}    //B

where nothing gets destroyed at //A but both get destroyed at //B

hmm I don't think this will quite work but I'll post it anyways to get more 
ideas.

- Michael Marcin