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Subject: Re: [boost] Is Boost.Range broken?
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2008-11-22 08:25:33

Tomas Puverle wrote:

> Here are the reasons why I think Boost.Range is broken:
> 1) Empty ranges are useless and they cannot even be reliably tested for
> emptiness. The empty() function now asserts and the is_singular() function
> behaves differently between debug and release builds, making it impossible to
> detect if a range is, in fact, empty. In addition, this is not documented well
> and can lead to subtle bugs and undefined behaviour, which will only manifest
> itself in release builds.
> 2) The behaviour is unintuitive. Range is a generalisation of the interface of
> the std::containers. With this change, containers and ranges can no longer be
> used in the same code path.
> 3) Reintroducing the "singular" member into release builds to make the
> is_singular() function work correctly will defeat the purpose of the size
> optimisation, while still not achieving interface compatibility with
> std::containers.
> 4) Having the additional if() condition in size() and empty()is unlikely to be a
> large burden on most programs. I would expect most programs will spend more
> time iterating data than testing ranges for emptiness.
> 5) The change could be reverted without affecting users. For those who are
> relying on the new behaviour, the change to empty() and size() should be
> immaterial, as they cannot be calling them now on singular ranges anyway.

This is a bad explanation which can prove misleading.

The reason why you think Boost.Range is broken is because iterator_range
(which is nothing more than a fancy std::pair, I never found the use of
it myself) used to allow operations such as "empty" on an uninitialized
range but doesn't anymore.

If it was just me, default-constructing iterators and ranges shouldn't
even be allowed (unless that is sufficient that initialize it).
A range that is not properly initialized is not in any usable state.
It's not an empty range, it's more like a pointer to somewhere random.
Just don't try to use it. If Boost.Range used to allow it, that was a
bug; good thing it is now fixed.

As for is_singular, that function shouldn't be exposed to the public.

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