[boost] Re: In-place construction for variant

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-29 19:19:02

"E. Gladyshev" <egladysh_at_[hidden]> writes:

> --- David Abrahams <dave_at_[hidden]> wrote:
> [...]
>> This problem doesn't change the fact that std::vector assignment gives
>> the basic guarantee.  Any class is allowed to break its own invariants
>> temporarily during the execution of its member functions.
>
> Well, I am completely confused about the whole
> basic guarantees stuff and its usefullness then.
> I just hope I am alone in this *undefined* state. :)

That a class' member functions may temporarily disturb its invariants
is a well-established principle that is accomodated even by languages
with built-in support for invariant checking.

> BTW: is there a "scientific" definition
> of what basic guarantees really are?

Can you give a "scientific" definition of what you mean by
"scientific?"  If you mean something suitable for use in a formal
proof of program correctness, the answer is no.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com