Re: [boost] [smart_ptr] shared_ptr template type

Subject: Re: [boost] [smart_ptr] shared_ptr template type
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2009-07-09 15:39:17

Frank Mori Hess wrote:

> On Thursday 09 July 2009, Andrey Semashev wrote:
>> Why not having monitor_ptr< T > contain the shared_ptr and implement
>> operator-> the way you described? 
> 
> Yes, that is in fact what I did:
> 
> http://www.comedi.org/projects/libpoet/boostbook/doc/boostbook/html/poet/monitor_ptr.html
> 
> However, it seems like more work to have to provide a full shared_ptr 
> interface, than to implement a plain pointer interface.

You don't have to reimplement shared_ptr interface, unless you really 
need it. And that interface isn't that sophisticated, anyway.

> And perhaps more 
> significantly, a monitor_ptr is a completely different type than a 
> shared_ptr.  So, for example, a monitor_ptr can't be passed to a function 
> that expects a shared_ptr as an argument.

Types shared_ptr<monitor<T*> >, shared_ptr<T*> and shared_ptr<T> are not 
compatible either, so you don't win here anything.

> Also, if there are other applications for pointer wrapper classes, they could 
> be mixed an matched in any combination by the end user in this scheme, like
> 
> shared_ptr<monitor<pointer_wrapper<T*> > >
> 
> Maybe, for example, a pointer wrapper class might  enforce that the wrapped 
> pointer may never be NULL, to implement a shared_ptr that acts something like 
> a "smart reference".

IMHO, one of the remarkable features of shared_ptr is its simplicity. 
All additional features that you describe, while being useful, are out 
of scope of this simple tool. I agree that some more elaborate 
policy-driven smart pointer would be useful to implement those things. 
It just isn't related to shared_ptr in any way. IIRC, Andrei 
Alexandrescu tried to develop such a pointer, I'm not sure how 
successful he was.