Re: [boost] [smart_ptr] shared_ptr template type

Subject: Re: [boost] [smart_ptr] shared_ptr template type
From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2009-07-09 13:54:54

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On Thursday 09 July 2009, Andrey Semashev wrote:
> Frank Mori Hess wrote:
> > I wonder if it might be better/possible to have a shared_ptr<T> that
> > didn't assume its corresponding "raw" pointer type was T* but rather T. 
> > For example, what is now a shared_ptr<int> would be specified as a
> > shared_ptr<int*>.  The motivation would be to allow support for other
> > classes as the "raw" pointer type.  For example, I might want to have a
> > shared_ptr<monitor<T*> > where the monitor<T*> has an operator->() which
> > does automatic locking/unlocking of a mutex before/after forwarding the
> > operator->() to the plain T pointer.
>
> 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.  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.

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".

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