Re: [boost] Request for consideration for my weak_ptr class

From: Marcus Lindblom (macke_at_[hidden])
Date: 2007-06-08 10:33:18

Alex Burton wrote:
> I understand there would be a collision with boost::weak_ptr, which is used for special scenarios with shared_ptr as I understand.
>   
Hm. checked_ptr, standard_ptr, regular_ptr, simple_ptr or just raw_ptr 
might be better names, to avoid collisions?

(The concept of a weak pointer or reference is quite common when used in 
garbage collection, as with boost::shared_ptr, so IMHO I would avoid 
that in general for non-gc pointer types.)
> A fair comment would be that this class actually does nothing, that a normal pointer would do and this is true.
> However, I find it extremely useful, and would like it considered as an addition to boost.
>   
Good initiative. However, there seems to be some orthogonal concepts 
baked in here, and everyone might not want all of them at the same time, 
even if each one is useful on their own. Perhaps each concept could be 
split up (via policy classes) so that one could define checks for any 
pointer?
> It allows my code to be free of the * pointer notation.
> All pointers look the same, ie shared_ptr<Foo>, scoped_ptr<Foo>, weak_ptr<Foo>
>   
Why is that desirable?
> It throws an exception if it has been default constructed or set to 0, this could probably be a debug only behaviour for efficiency, but i leave it in release code.
>   
I find the notion of a null ptr useful. How about just checking that in 
operator * and -> as other boost::ptr's.

Unless actually do want a nonnull_ptr, but that should be optional. 
(boost::ahared_ptr's can be
> It can be used in many places a reference would be used.
>   
I don't get this one. It's not a smart reference, a smart pointer?
> It includes constructors for many smart pointer types and from a reference to the class pointed to.
>   
Useful. However, you might want to consider a unqualified get_pointer() 
call to allow for any smart pointer (including my secret one that I 
won't show you :-). Also, less constructors. (as for get_pointer(), I 
believe boost::bind and others uses it to get the raw-pointer from any 
type, including references)
> using namespace std;
>
> struct IFoo
> {
> };
>
> struct Foo : IFoo
> {
> };
>
> vector<Foo> foos;
>
> BOOST_FOREACH(weak_ptr<Foo> f,foos)
> {
>     //do something with f->
> }
>
> vector< weak_ptr<IFoo> > weakfoos;
> std::copy(foos.begin(),foos.end(),back_inserter(weakfoos));
>
> In the above code, if vector<Foo> foos was changed to vector< shared_ptr<Foo> > the code will still work perfectly with out change.
>
> I find this really useful because often small structs become polymorphic classes (requiring shared_ptr) as code evolves.
>   
Yup. I see where that could be useful. 

OTOH, the for_each could use an indirect_iterator-range instead, to 
iterate over IFoo& instead.

Cheers,
/Marcus