Re: [boost] Proposal to add smart_ptr to the boost library

From: David Maisonave (dmaisonave_at_[hidden])
Date: 2006-01-31 11:39:01

"Sam Partington" <sam.partington_at_[hidden]> wrote in message
news:<546fdb840601310328m7480d265u49afde5a1fd85cfa_at_[hidden]>...

> class A
> {
> public:
>   A()
>     : l(m, false)
>   {
>   }
> 
>   void lock() { l.lock(); }
>   void unlock() { l.unlock(); }
> 
> private:
>   mutable boost::mutex m
>   boost::scoped_lock l;
> };
> 
> void intrusive_ptr_lock(A * p)    { p->lock(); };
> void intrusive_ptr_unlock(A * p) { p->unlock(); }
> 
> ...
> 
> smart_ptr<A, copy_on_write_policy<intrusive_lock_policy> > ptr(new A);
> 
> Thats quite a lot of work, though some of the problem with that is 
> probably down to the way boost::mutexes are handled.

I'm still considering adding a lock policy that will only work with
reference-count and deep_copy, and that will not require intrusive
logic.
That would make the usage more generic, but not as efficient as
instrusive lock.

> std::auto_ptr
> std::tr1::scoped_ptr
> std::tr1::shared_ptr
> boost::cow_ptr ?
> boost::copy_ptr ?
> 
> Should be sufficient for most needs? and everyone one of them is a
> hell of a lot easier to type than :
> 
> boost::smart_ptr<A,
> boost::copy_on_write_policy<boost::intrusive_lock_policy> >
> 

One thing I really like about the current proposed boost::policy_ptr, is
that you can do a typedef on the policy.
Example:
typedef boost::smart_ptr<boost::ref_linked> MySharedPtrRefLnk;

MySharedPtrRefLnk::to<Shape> pShape;

So if you don't like all that typing, you can just do a typedef for the
type you expect to use in your project.
My propose smart_ptr doesn't have such an elegant method as the proposed
policy_ptr, but it does have the following:
typedef smart_ptr_type<copy_on_write_policy<intrusive_lock_policy> >
MyCowSyncSmartPtr;
MyCowSyncSmartPtr::to<Shape>::type pShape;

I plan to take a look at the policy_ptr, to see how they're going about
avoiding the ::type part.