Re: [sigc] sigc::trackable::~trackable() is not virtual

[Ulrich Eckhardt <eckhardt satorlaser com>]

On Thursday 26 October 2006 17:19, stephan beal wrote:
> You're relying on UNDEFINED BEHAVIOUR when you
> subclass a type which doesn't have a virtual dtor.

Wait, that statement as it stands is not true. You invoke UB if you delete an 
object through a pointer to base if said base doesn't have a virtual dtor. 
IOW, the rule is to use a virtual dtor in the baseclass if you plan to 
polymorphically delete objects through a pointer to the baseclass. 

Now, another rule say that therefore you should either use a public, virtual 
ctor or a protected, non-virtual one, which is the second solution to the 
problem.

However, polymorphic delete is not the case the designers envisioned for 
sigc::trackable. Deriving from sigc::trackable is rather an implementation 
artifact of sigc, making syntax simpler because you can retrieve the helper 
for tracking connections by simply converting an object to its 
sigc::trackable baseclass. I'm not sure this really requires that the dtor be 
public, have you tried making it protected?

Uli

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