Re: [boost] Re: In-place construction for variant

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-11-03 16:43:46

--- David Abrahams <dave_at_[hidden]> wrote:
> "E. Gladyshev" <egladysh_at_[hidden]> writes:
> 
> >> This has *nothing* whatsoever to do with the basic guarantee, other
> >> than that the basic guarantee is phrased in terms of invariants.  Any
> >> condition arising from this fact that you can conjure up with
> >> exceptions can also be created without them.  I suggest you drop
> >> discussion of the basic guarantee and exceptions for the time being and
> >> just look at invariants in stateful programming.
> >
> > The point of my question was how to use basic guarantees 
> > in practice especially in case of an exception.  
> > Usually I am making two assumptions.
> > If there is an an exception then:
> > 1. There is a problem with the hardware.
> > 2. The program is incorrect and the invariants,
> >    integrity of the memory and program stack can be broken.
> > In both cases, I don't think that it is safe to do anything.
> 
> Right.  But both those assumptions are in general wrong.  Exceptions
> are thrown when postconditions can't be satisfied ("I can't allocate
> enough memory to resize this vector"), not when something's
> fundamentally broken in the program or hardware.

Ok, but how do you differentiate "fundamentally-broken"
exceptions from "good" exceptions in your code?

> 
> > Do program invariants or basic guarantees change anything 
> > in how you handle exceptions?
> 
> I don't understand the question.

As far as I understand basic guarantees make it possible
to use objects in case of an exception.

//my_type provides basic guarantees.
my_type *p = new my_type;

try
{
  p->f();
}
catch(...)
{
  //basic guarantees allow you to delete 'p' safely!!!
  delete p; 
}

Is it *really* safe to delete 'p' even if it provides
basic guarantees?
We agreed (?) that the program my be "fundamentally" broken
at the time when we caught the exception.

Eugene

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