Re: [boost] deleting smart pointer

Subject: Re: [boost] deleting smart pointer
From: pavel (paul.cpprules_at_[hidden])
Date: 2011-03-20 05:30:16

 Steven wrote on Saturday, March 19, 2011 at 18:40:26:
> Actually, I got it from n3242 which is a recent C++0x draft.

are you sure that this draft is going to become the final version of
std? if so further discussion is pointless since the std kills the
very opportunity to implement such a feature (and some custom
allocation strategies as well) 

> Okay. Let's do this a different way
> (a little later in the section):

> "In the first alternative (delete object), if the static type
> of the operand is different from its dynamic type, the
> static type shall be a base class of the operand’s
> dynamic type and the static type shall have a virtual
> destructor or the behavior is undefined."

i believe this part concerns slicing as when one deletes an object of
some derived class D using pointer to the base class B

this way ~D() destructor has no chance to be executed and we have the
whole bunch of unwanted effects

furthermore when '::delete operator()' function is called the compiler
may miscalculate the size of the object to be deleted since sizeof(D)
may differ from sizeof(B) and the deallocation function likely be
supplied with wrong size argument which again may cause unexpected
effects 

in my variant of implementation all destructors involved are trivial
(read: they are never called) and the global deallocation function
('::operator delete()') is never called on the operand of the delete
expression

so i believe it shouldn't cause undefined behavior anyway

-- 
Pavel
P.S.
if you notice a grammar mistake or weird phrasing in my message
please point it out