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Subject: Re: [boost] Breaking existing libraries
From: David Abrahams (dave_at_[hidden])
Date: 2008-11-25 11:43:57

Sent from my iPhone

On Nov 25, 2008, at 10:40 AM, "Neil Groves" <neil_at_[hidden]>

> Thorsten,
> I think the majority of opinions on this thread have voiced a
> preference for
> the old behaviour because singularity is a property of an iterator,
> not a
> range. Adding the validity constraint imposes too many restrictions
> upon
> otherwise valid uses of default constructed iterator_ranges where the
> iterator provides stronger guarantees.

You don't need the old behavior (which attempted to provide those
guarantees even when the underlying iterators can't, at the cost of
space and time) to have that.

> In my opinion, the Range concept should not have 'singular'.

Protecting users from singular iterators at the cost of space and
time, especially in those cases when the iteratirs themselves already
provide a nonsingular default-constructed state, of a bad idea.

> I appreciate that there were previous discussions prior to your
> change, but
> under firther scrutiny it appears that the wrong conclusion was
> reached.
> On Tue, Nov 25, 2008 at 3:30 PM, Thorsten Ottosen
> <nesotto_at_[hidden]> wrote:
>> Tomas Puverle skrev:
>>> If the compromise does not include going back to the old behavior
>>> for
>>>> boost::iterator_range, then I'm open to suggestions
>>> (Joke intended)
>>> This really doesn't seem to meet the criteria for a "compromise".
>>> Just sounds like you're getting your way.
> Perhaps erroneous use of singular iterators could be added through
> improvements to iterator debugging facilities?
>> Why? I'm open to including a new class with the old behavior, even
>> though I
>> think it has little purpose.
> I don't think two classes that are almost identical is worthwhile. The
> singularity validation does not serve enough useful purpose to
> justify the
> limitations, and space overhead. Singularity debugging does not
> belong here.
>> Wha compromise did you have in mind?
>> -Thorsten
> Neil Groves
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