[boost] Re: Exception safety guarantie

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-18 02:18:48

"David B. Held" <dheld_at_[hidden]> writes:

> David Abrahams wrote:
>
>>[...]
>>>Ah, but you yourself have said that the guarantees do not form a
>>>hierarchy, so there is no proper notion of "stronger" with respect
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>  >>to them. ;)
     ^^^^^^^^
>> Whaaaa???  I never said that!  Or I was delusional when I did.
>
> Well, perhaps you remember a thread in which I suggested another
> guarantee that I called the "smart guarantee" which was a cross
> between the strong and the basic guarantee.  You argued that one
> could invent any number of guarantees that offer different promises
> and which could not be ordered in any purely objective way.  It was
> a fairly convincing argument at the time.  Are you going to retract
> it? ;>

Not at all.  But I never said the marked thing above.  Certainly any
guarantee that only adds requirements to another is stronger.  It's a
partial order.  There are plenty of pairs of guarantees that have an
ordering relationship, and plenty of others that don't.

>>[...]
>>>Saying that it maintains its invariants instead of saying that it
>>>gives the basic guarantee does not convey the right message, in my
>>>opinion, because many programmers obviously do not feel a need to
>>>maintain invariants in the presence of exceptions (or they would write
>>>more exception-safe code).
>> I don't see the connection.  What message do you think it should
>> send
>> that it does not send?
>
> That it maintains invariants *in the presence of exceptions*.  

Quoting my original suggestion:

>> ...
>>   The library maintains its invariants and does not leak resources
>>   in the face of exceptions.  Some library operations give stronger
     ^^^^^^^^^^^^^^^^^^^^^^^^^
>> ...

Perhaps we have an "and" associativity/ambiguity problem here?
It meant the same as this when I wrote it:    ;-)

   In the face of exceptions, the library maintains its invariants and
   does not leak resources.

> The latter part is implicit, but if the user isn't thinking in terms
> of exception safety to begin with, then they may well miss that
> part.  When you say "provides the basic guarantee", if the user is
> not familiar with exception safety, she will at least have an
> opportunity to investigate it.  Of course, you could just say both.

Which is what I suggested in another message.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com