Re: [Boost-users] Library Interface Design

From: David Abrahams (dave_at_[hidden])
Date: 2006-09-14 14:33:35

Brian Allison <brian_at_[hidden]> writes:

> David Abrahams wrote:
>
>>"Peter Dimov" <pdimov_at_[hidden]> writes:
>>
>>  
>>
>>>No, a singular iterator is not a valid object and it fulfills no
>>>invariants. 
>>>    
>>>
>>
>>That's arguable.  From my POV, if it's in a state that a legal program
>>can create, it's within the invariant by definition.
>>
>>  
>>
>
> Then (if I read you correctly) even undefined behavior is within the 
> invariant? 

No, invariants are about state and UB is about behavior.  Behaviors
don't fall inside or outside of states.

> Or have I been misunderstanding that legal programs can cause UB?

I don't understand the question, sorry.

When a program causes undefined behavior, that falls into the category
I'm calling "illegal program."  I don't just mean those programs that
can be diagnosed as illegal by the compiler.

> I've always considered that UB is to be treated as "not maintaining 
> the invariant but it's not my fault".

By whom?

> But then, whether we consider UB within the invariant (and hence
> that an iterator is by definition always within the invariant) or
> whether we consider UB outisde of the invariant but one which
> doesn't break correctness (and hence that unassigned iterators are
> not capable of being within/outside of an invariant)....
>
>   ... is there any practical difference between those two points of view?

Sorry, this whole behavior-within/without-the-invariant concept
doesn't make any sense to me.  It's probably just my too-literal mind
at work, but if you could rephrase or explain maybe I could answer.

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