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 16:15:57

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On Thursday 09 July 2009, Andrey Semashev wrote:
> Frank Mori Hess wrote:
> > 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.

That's mostly true, however suppose you have a function like

template<typename T>
myfunc(shared_ptr<T> sp);

You might say it could be replaced with something more generic like

template<typename SharedPtr>
myfunc(SharedPtr sp);

but perhaps myfunc creates a weak_ptr<T> from the incoming parameter.  The 
more generic version won't work because shared_ptr doesn't include a typedef 
for its corresponding weak_ptr type.  Also, the more generic version of 
myfunc might cause conflicts if myfunc has other overloads.  You'd be forced 
to add specialized code for each additional shared_ptr-like class you 
introduce, or something like type traits for them.
 
> IMHO, one of the remarkable features of shared_ptr is its simplicity.

I agree.

> 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. 

Perhaps I should have distanced my idea from shared_ptr more in presenting it, 
as I know making interface changes to shared_ptr is almost unthinkable at 
this point.  But it's obviously a related idea, in that 
generalized_shared<T*> would be equivalent to shared_ptr<T>.  And also I 
imagine generalized_shared could be implemented by copying the entire 
shared_ptr codebase and then making only minor changes.

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