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

From: Michael Anderson (michael.anderson_at_[hidden])
Date: 2007-03-01 21:09:21

Peter Dimov wrote:
>> So the solution I've come up with means that the Foo object only gets
>> destroyed when both the barptr and the fooptr are destroyed.
>> Unfortunately this requires additions to the shared_ptr class (the
>> patch is below). The changes are _very_ similar to what is used for
>> handling the pointer conversions and casts.
> 
> There has been a formal proposal to add an "aliasing constructor" (as in 
> your patch, but public and without the tag) to std::tr1::shared_ptr and I'm 
> considering adding one for 1.35. 

That's nice to hear, as a few other people inside my company have 
mentioned that such a feature would be useful to them. (and we'd rather 
not patch our copies of the boost libraries)

> In the meantime, 
... snip ...
 > you can use:
> 
> template<class T, class M> shared_ptr<M> member_pointer(
> shared_ptr<T> const & t, M* m)
> {
>     return shared_ptr<M>( m, bind( &shared_ptr<T>::reset, t ) );
> }
> 

This seems to work perfectly.
One thing to note is that this solution uses extra memory for storing an 
internal copy of the boost shared pointer and the custom deleter.

 > A similar trick is described in:
 >
 > http://www.boost.org/libs/smart_ptr/sp_techniques.html#another_sp

This is nifty as it lets you get back to the parent pointer if you want, 
but is essentially the same as the method outlined above (not a 
criticism, just a note for those who dont want to follow the link)

So in summary: these are both great solutions, but I feel that an 
aliasing constructor would be a great addition to the boost shared 
pointers library.

Thanks,

Michael Anderson