Re: 2nd: [boost] shared_ptr proposal

From: Christian Thäter (chth_at_[hidden])
Date: 2001-07-12 17:30:36

> 
> This comes up enough that I've added a FAQ entry:
> 
>    Q. Why doesn't shared_ptr use a linked list implementation?
>    A. A linked list implementation does not offer enough advantages
>       to offset the added cost of an extra pointer.  See timings page.
> 
> I've also added a reference to one of the other FAQ entries:
> 
>    (Those interested in policy based smart pointers should read Modern
>    C++ Design by Andrei Alexandrescu.)
> 
> If you look at the Smart Pointer Timings 
> http://www.boost.org/libs/smart_ptr/smarttests.htm, the real questions
are:
> 
> Why haven't we added an allocator to shared_ptr?
> 
> Why haven't we proposed an invasive_shared_ptr?
> 
> While there are some technical issues, I'm afraid part of the answer is 
> simple inertia.  And of course shared_ptr as it now stands is plenty
good 
> enough for the majority of uses.
> 

Sure i agree that there possible more efficient implementations. 
My point was not concerning the implementation. I want to focus on the
semantic and if we agree on some semantic, then think about the best
implemetation. Actually we have the simple and efficent std::auto_ptr with
it's ownership-transistion and boost::shared_ptr whith it's lossy
(on reset/assign) semantic's.
So the question is, "Is there a need for other semantics?", like: 
"Shall it ensure strict resource sharing which keeps track of
reset/assign operations for all instances of a pointer?"
"Shall pointer-construction have predictable timing behaviour?"
"Shall pointer construction never throw?"

I believe that future C++ needs more high-level support with no
side-effect's in it's semantics, at least optional. Sure building smarter
things often involves higher cost, but on the advantage of easier use of
the components. So, I experimented the last days a bit with these
pointers, learned alot about the important points, now I implement the
linked_ptr and linked_array classes according to the boost/smart_ptr
interfaces for my own use, if anyone is intrested i can send/post/upload
the source.

cya Christian