Re: [boost] Is there any interest in a library that provides cont ainers with virtual destructors?

From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2005-10-26 09:31:37

----Original Message----
From: Victor A. Wagner Jr. [mailto:vawjr_at_[hidden]]
Sent: 26 October 2005 15:16
To: boost_at_[hidden]; 'boost_at_[hidden]'
Subject: Re: [boost] Is there any interest in a library that provides
cont ainers with virtual destructors? 

> At 02:51 2005-10-26, Martin Bonner wrote:
>> ----Original Message----
>> From: Victor A. Wagner Jr. [mailto:vawjr_at_[hidden]]
>> Sent: 26 October 2005 05:36
>> To: boost_at_[hidden]; boost_at_[hidden]
>> Subject: Re: [boost] Is there any interest in a library that provides
>> containers with virtual destructors?
>> 
>>> At 10:04 2005-10-25, Andy Tompkins wrote:
>>>> I have read a few times that people sometimes wish that std::vector
>>>> (or other containers) had a virtual destructor. [snip]
>>>> This allows one to write something like:
>>>> 
>>>> struct person {
>>>>   string first_name;
>>>>   string last_name;
>>>> };
>>>> class people : public virtual_vector<person>
>>>> {
>>>> public:
>>>>   //extra methods
>>>> };
>>>> 
>>>> Is this useful?
>>> 
>>> unless I mis-read (or mis-understood...far more likely) a lot of
>>> books on how C++ works, I don't believe there is any reason for what
>>> _you've_ shown to need a virtual destructor.
>> 
>> You have mis-read or mis-understood (or you need better books). 
>>     Consider: virtual_vector<person>* p = new people;
> 
> I guees I wasn't clear..  I was suggesting that virtual_vector has no
> need for existence.
> 
>>     delete p;
>> That invokes undefined behaviour unless virtual_vector<person> has a
>> virtual destructor.
> 
> are you suggesting that if it were   class people: public
> std::vector<person> {.....};  as above the same would be true?
> not "in practice", "in theory".

Absolutely.  See 5.3.5/1 of the standard where this is explicitly called out
as undefined behaviour.

-- 
Martin Bonner
Martin.Bonner_at_[hidden]
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ,
ENGLAND Tel: [phone]