Re: [Boost-users] Boost range changes [1.37.0]

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?

-Thorsten