Re: out_ptr review is extended until Wednesday, July 10

From: JeanHeyd Meneide (phdofthehouse_at_[hidden])
Date: 2019-06-27 04:12:17

On Wed, Jun 26, 2019 at 11:05 PM Gavin Lambert via Boost <
boost_at_[hidden]> wrote:

> On 27/06/2019 13:52, Bagaskoro Kang wrote:
> > the creator apis  have two out params:  Interface** pointer and
> unsigned*
> > size and the  destroyer functions must be called with pointer and the
> size.
> >
> >      Interface** obj;
> >      unsigned size;
> >      int ret = Create(... ... ... &obj, &size);
> >
> > and  then we need to call a Release(obj, size) if the ret is success.
> >
> > I do not think I can use the out_ptr with these APIs ???
>
>
struct sized_deleter {
    unsigned size;
    ...
};

using bop = boost::out_ptr;

std::unique_ptr<Interface, sized_deleter> p_obj;
int ret = Create(..., bop::out_ptr(p_obj), &p_obj.get_deleter().size)
if (LIBNAME_HAS_FAILED(ret)) {
     throw std::runtime_error("deep sadness");
}

This example is less pretty because I'm putting the size in the deleter,
but it works.

> > also we call the Linux kernel C  API posix_memalign() and we assign to
> > unique_ptr. is not possible to use out_ptr with ?
> >
> >      std::unique_ptr<Numf, DoFree> upNumf;
> >      void  * pNumf;
> >      int ret = posix_memalign(&pNumf, 64, nNumf);
> >      if (!ret)
> >          upNumf.reset((Numf*)pNumf);
>

using bop = boost::out_ptr;

std::unique_ptr<Numf, DoFree> upNumf;
int ret = posix_memalign(bop::out_ptr<void*>(upNumf), 64, nNumf);
if (ret != 0) {
     throw std::runtime_error("something went wrong, but at least we're not
leaking memory here.");
}

Casting support is built in to the API: you can go from strongly typed
pointers to void**, or other related pointers by passing the type as a
template argument.