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Subject: Re: [Boost-users] Boost range changes [1.37.0]
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-11-19 17:15:43

Tomas Puverle skrev:
> I just upgraded from Boost 1.33.1 to 1.37.0 and have found a breaking change in
> Boost.Range.
> Previously, iterator_range::empty() would do the following:
> bool empty() const
> {
> if( singular )
> return true;
> return m_Begin == m_End;
> }
> and similarly for size(). In the new release, instead of the test, there is an
> assertion, which is now breaking my code.
> Why (and when?) was this change introduced? This make Boost Range much in
> generic code, such as
> template<class Range>
> void foo(const Range & r_)
> {
> if (r_.empty()) {...}
> }
> The code is frequently called with containers and ranges and works beautifully.
> However, a common pattern is to call the function with a default constructed
> (empty range). This now crashes. The only way to test for validity AFAICS is
> to call is_singular(), unfortunately, this breaks when the function is called
> with containers.
> This, IMHO, was an unfortunate decision. Any suggestions anyone?

The change has happened long ago. It was a design mistake to try to make
a range of singular iterators valid since it adds overhead also for
those that don't need it.

Your use-case is new to me, but seems quite ok. But making
boost::iterator_range as a mixture of a range and boost.optional seems
like a bad idea.

template<class Range>
void foo(boost::optional<const Range &> r_)
   if (r && !r_->empty()) {...}

might be an idea?


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