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Re: [smart_ptr] shared_ptr template type
by Andrey Semashev-2
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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.
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> 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.
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