Re: [boost] [inplace_factory] Question about nplace_factory

From: Corrado Zoccolo (czoccolo_at_[hidden])
Date: 2007-11-18 04:57:15

Hi Fernando,

> It clearly could, though it worries me than in that case it wouldn't be an
> "in-place" factory but just a ordinary factory.
> While I can understand your need from your side, specially assuming that
> the
> pointer is an implementation detail, it feels a bit of a hack from the
> in-place factory POV.
>

Ok, but I think having it could improve in_place factory usability in
several places. I'm not the only one working on a library proposal with
small object optimization currently. Maybe also Steven's TypeErasure library
could benefit from this.

> <snip>
>  IIRC
> typical implementations of new call malloc() then in place new, so,
> couldn't
> you do the same?
>

I can call either malloc or global new (both will give correctly aligned
memory), but this will defeat class specific memory management.
If operator new and delete are redefined for a given class, I'd like to (and
the library user also would me to) use the redefined one.

Moreover, if new/delete are redefined, the memory allocated by:
 void *b=::operator new (sizeof T); // memory allocated through global
operator new
 p= new (b) T(args);  // this is what in_place does
cannot be deallocated by
 delete p;

I think something like the following should work, but it seems clumsy and I
still have to check:

template<typename T>
struct new_invoker : T {
 static void * alloc() { return operator new(sizeof T); } // should look up
operator new in T scope before global scope
 static void dealloc(void *p) { return operator delete(p); } // should look
up operator delete in T scope before global scope
private:
 new_invoker();
 new_invoker(new_invoker const &);
 void ~new_invoker();
};
// specializations for non-class types omitted

Corrado

-- 
__________________________________________________________________________
dott. Corrado Zoccolo                          mailto:zoccolo_at_[hidden]
PhD - Department of Computer Science - University of Pisa, Italy
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