[Bug libstdc++/15523] Can't have vectors of vector::const_iterator

["llewelly at xmission dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From llewelly at xmission dot com  2004-05-19 17:32 -------
Subject: Re:  Can't have vectors of vector::const_iterator

"bangerth at dealii dot org" <gcc-bugzilla@gcc.gnu.org> writes:

> ------- Additional Comments From bangerth at dealii dot org  2004-05-19 14:24 -------
> I see your point, although 24.1/5 only speaks about "most operations" and 
> does not specifically rule out that we do the sensible thing here. I 
> think my point is that I fail to see the value of this check, since it 
> seems to be allowed to create such an iterator, but not to copy it. On 
> the other hand, if we simply omitted the check we would fall over later 
> if we ever tried to dereference it. The only thing that one would have 
> to make sure is that the result of assigning a singular iterator to 
> another iterator is again a singular iterator, but that should be what 
> happens anyway if we simply copy all member variables. 
>  
> I don't feel strongly either way, since I already fixed my code to 
> work around this, but I do feel that there are cases where one would 
> like to generate a vector of singular iterators, and only after that 
> assign individual values to them. 

The obvious answer is that if one can't initialize a vector of
    iterators to the 'right' value, one should initialize them to the
    null iterator. :-) (I know, pointers are the only iterators for
    which such a value exists.)

I think in most cases it would be sufficient to create an empty
    vector, set it its vector<>::capacity(), and then push_back() new
    values into it.

My naive expectation would be that -D_GLIBCXX_DEBUG_PEDANTIC would
    cause an abort() for all dectectable undefined behavior. I think
    most other users would expect this as well, *but* many probably
    don't realize this extends to aborting on the copy of a singular
    iterator, much less to aborting on the creation of the vector full
    of singular iterators. OTOH, some users expect implementations to
    report errors they don't know about.
    


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15523