From: Daniel Krügler (dsp_at_[hidden])
Date: 2008-06-25 06:00:23
John wrote:
> Thorsten Ottosen wrote:
>
>> John skrev:
>>
>>> This pattern/idiom is well-established:
>>>
>>> struct A {
>>> virtual A* clone () = 0;
>>> };
>>>
>>> struct B : public A {
>>> virtual B* clone ();
>>> };
>>>
>>>
>>> But the above does not work when the pointers A* and B* are replaced
>>> by shared_ptr<A> and shared_ptr<B>:
>>>
>>> struct A {
>>> virtual shared_ptr<A> clone () = 0;
>>> };
>>>
>>> struct B : public A {
>>> virtual shared_ptr<B> clone ();
>>> };
>>>
>>>
>>> Is there a workaround? Another way to solve the same problem? Thanks!
>>
>>
>> Well, don't use shared_ptr here. A newly created clone is not shared,
>> and it makes the interface less usable in other context to return a
>> shared ptr here.
>>
>> -Thorsten
>
>
>
> Hah! Well, yes, I guess it's true that there's always an option not to
> use smart pointers at all. :) Perhaps people will make too many
> assumptions about the method based on the name, "clone". Instead,
> pretend the clone() method is named something else, without any other
> assumptions.
>
> For example, pretend it's a get_row() method for a database cursor
> abstraction. The method might trigger a fetch, in which case the
> returned object is not shared, or it might return a previously fecthed
> row. Also, whether this method is usable in non-smart-pointer context
> is not a concern. -John
If you are interested in a more generalized approach of the same
problem, you should have alook at
http://preview.tinyurl.com/3w6elg
Greetings from Bremen,
Daniel Krügler