[C++-sig] Re: (no subject)

[David Abrahams]

Raoul Gough <RaoulGough at yahoo.co.uk> writes:

> David Abrahams <dave at boost-consulting.com> writes:
>
>> Raoul Gough <RaoulGough at yahoo.co.uk> writes:
> [snip]
>>> Using this approach would cause me to worry about object slicing (C++
>>> object slicing, I mean) since I would probably tend to pass and
>>> certainly return reference objects by value. I suppose the base class
>>> would actually be equipped to handle everything internally, but I
>>> would *usually* assume that the following code is wrong:
>>>
>>> reference make_python_object () {
>>>   return new_reference (/*...*/);  // Slices object on return
>>> }
>>
>> There's nothing wrong with "slicing".  Its dangers are vastly
>> overrated.  Think of it as an implicit conversion operator.
>
> I don't think I overrate the dangers of slicing - they are real and
> should be considered when slicing happens. Pass or return by value
> could be totally wrong, depending on the implementation details. For
> instance, assume that ~reference() does nothing, and only
> ~new_reference() does a Py_DECREF. This would be a workable
> implementation, and would mean that borrowed_reference doesn't have to
> increment the reference count to compensate for the base class
> destructor. Unfortunately, returning the base-class part of a
> new_reference object would then delete the target object
> immediately. I guess my point is that without investigating further,
> somebody reading the code can't tell if the slicing is benign or
> not.

OK, good point.

>> Well, my point was that I thought it was more useful and safer to
>> encode the acquisition method in the type.
>>
>> Could be wrong, though.
>
> It also seems safer to me, since the base class constructor is
> protected. On the other hand, maybe removing the plain pointer
> overload for handle<>::handle() would be just as good?

Can't do that without providing a new_reference(...) wrapper.

> -- 
> Raoul Gough.
> (setq dabbrev-case-fold-search nil)

Interesting sig.  Do you want me to `C-x C-e' it?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com