On 12/07/12 09:15, tolik levchik wrote:
Why min_element give me errors without BOOST_RANGE_ENABLE_CONCEPT_ASSERT defined 0? Is it uses only for make error messages more readable? Is it   safe to define it to 0?

Firstly, it is definitely safe to consistently define BOOST_RANGE_ENABLE_CONCEPT_ASSERT as 0. This will disable concept checking within Boost.Range. The intent of the concept checking is two-fold. It will detect usage errors at compile-time that in some cases may become run-time errors without the checks. It also provides better error messages close to the location of the error.

#include <vector>
//#define BOOST_RANGE_ENABLE_CONCEPT_ASSERT 0
#include <boost/range.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/algorithm.hpp>
#include <boost/range/numeric.hpp>
#include <boost/bind.hpp>

struct foo{
int x;
};

int main()
{
using namespace boost::adaptors; using boost::bind;

std::vector<foo> vec;
auto rng = vec | transformed(bind(&foo::x, _1));
boost::accumulate(rng, 0); // ok 
boost::min_element(rng); // error
}

I suspect that the underlying transform_iterator alters the return type of the dereference operator that technically demotes the iterator category.

If this is the case then this is a defect in the Boost.Range library that I shall need to address. I should have used the Boost iterator traversal categories.

I shall look into this. Thank you for the report.

Regards,
Neil Groves