[boost] Re: checked_delete without assignment to 0 - why?

From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2003-05-15 07:18:48

Gennaro Prota wrote:

> [...] 

> nullifying the pointer is generally considered 
> a way to _hide_ bugs, 

I doubt Herb Sutter hides bugs.
sed -es/generally considered/IMHO/g

> rather than eliminating them. I don't want to be dogmatic
> here, but I've never encountered the necessity to double delete
> anything.

It is not about double delete, but about code which 
is guaranteed to check some pointer for equality with 0 
before use:

E.g. in my application it is cheaper to run over a 
fixed-sized vector of pointers rather than using a container 
holding only the ones pointing to accessible data.

This is where a simple deletion is insufficient and nullifying 
is _not_ hiding bugs, but the correct way to express
a _complete_ destruction/erasure alias a true zero.
Any use of smart pointers in that place multiplies the 
runtime by inacceptable factors, so the use of raw pointers 
and DeleteAndNullify is _the_ thing to do.

Therefore I was thinking of re-using something like 
boost::checked_delete, and simply curious about why the 
assignment was omitted, which was the reason for the OP. 
 
After taking a closer look at the boost::smart_pointer's code
I can finally see they never rely on the "value" of the raw 
pointer after its deletion and therefore it is perfectly OK 
to avoid additional assignment in checked_delete for the sake of 
efficiency.

OTOH, since I think 
template <typename T> void delete_and_null(T*& p);
is a useful function I would propose it for inclusion into boost.

Markus

P.S.: Thank You for pointing me to alt.comp.lang.learn.c-c++,
but I doubt they tell me the reason for design or naming decisions 
in the boost library ;-). 

-- 
Compile time analytic differentiation? 
Yes, at http://daixtrose.sourceforge.net/