Re: EBCO - why does it require inheritance?
On Aug 22, 8:17 am, Joe Greer <jgr...@doubletake.com> wrote:
Chris Fairles <chris.fair...@gmail.com> wrote innews:1187716997.858600.229750@g4g2000hsf.googlegroups.com:
This all came about while implementing unique_ptr for c++0x.
template <class _Tp>
struct default_delete : public unary_function<_Tp*,void> {
default_delete() {}
template <class _Up> default_delete(const default_delete<_Up>&) {}
void operator()(_Tp* __ptr) const {
static_assert(sizeof(_Tp) > 0, "can't delete pointer to incomplete
type");
delete __ptr;
}
};
template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */
_Tp* __ptr;
_Tp_Deleter __deleter;
};
Given the nature of your deleter's, you can either make the method static like:
template <class _Tp>
struct default_delete : public unary_function<_Tp*,void> {
default_delete() {} template <class _Up> default_delete(const default_delete
_Up>&) {}
static void delete(_Tp* __ptr) const {
static_assert(sizeof(_Tp) > 0, "can't delete pointer to incomplete
type");
delete __ptr;
}
};
template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */
_Tp* __ptr;
~unique_ptr() { _Tp_Deleter::delete(__ptr); }
};
A good idea, but I don't think this will work when considering user-
defined deleters. It would require deleters to have a static function
but the standard allows the deleter to have non-static state that can
be accessed within the member func (operator or not) that does the
delete.
or you can instatiate it when you need it rather than at construction time.
template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */
_Tp* __ptr;
~unique_ptr() { _Tp_Deleter()(__ptr); }
};
Again, due to deleters having state, and unique_ptr's being able to
store references to deleters, the following is well formed:
struct deleter
{
deleter(std::string msg):m(msg){}
void operator()(int *) {std::cout << msg; delete i;}
std::string m;
};
deleter d("hi mom");
std::unique_ptr<int,deleter&>(new int, d);
//or std::unique_ptr<int,deleter>(new int, deleter("hi mom")) etc.
So instantiation-on-use won't work so long as the above is allowed.
Just some thoughts,
Much appreciated.
Chris