[boost] Re: Deadline for the Standard Library TechnicalReport

From: Andrei Alexandrescu (andrewalex_at_[hidden])
Date: 2003-01-28 11:37:19

"Peter Dimov" <pdimov_at_[hidden]> wrote in message
news:00b201c2c6da$16c22e70$1d00a8c0_at_pdimov2...
> From: "Andrei Alexandrescu" <andrewalex_at_[hidden]>
> [...]
> >
> > It should be noted that the constructor taking a custom deleter has many
> > implementation efficiency consequences that are not mentioned in the
> > Standards proposal nor in the shared_ptr doc. My feeling is that the
> > documentation at
> > http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1397.html and at
> > http://www.boost.org/libs/smart_ptr/shared_ptr.htm is coy about
mentioning
> > that the added constructor requires quite some more overhead under the
> > covers, including runtime polymorpshim, virtual calls, extra
allocations,
> > all those good things.
>
> The runtime polymorphism/virtual call issue is not exclusively mandated by
> the two-argument constructor. It is necessary to capture the deallocation
> information at construction time in order to support incomplete classes,
> EXE/DLL heap mismatch, and shared_ptr<T>'s ability to call the right
> destructor regardless of T.

I understand that. I also know not all people would need all that.

[...]
> I really don't understand why you consider policy-based smart pointers and
> the current shared_ptr enemies, when in my opinion they perfectly
complement
> each other. But I've grown tired of asking.

I guess I started feeling that way when I've been told that shared_ptr is
everything everyone will ever need, so there's no need for policy-based
smart pointers :o).

In a language with template typedefs, there would be no complementarity -
shared_ptr will be but one point in the design space allowed by smart_ptr.

Andrei