Compilation error when using boost::phoenix with range adaptors

[Nicolas Savoire <nicos@…>]

The following piece of code fails to compile with gcc-4.5:

#include <iostream>
#include <boost/range.hpp>
#include <boost/range/irange.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/phoenix.hpp>

using namespace boost::phoenix::arg_names;
using namespace boost::adaptors;

int main()
{
  std::cout << *boost::begin(boost::irange(0,5) | transformed( arg1 +1));
}

The error is:

In file included from /usr/local/mkt-dev/src/boost_1_47_0_rc/boost/range/adaptor/transformed.hpp:16:0,
                 from /usr/local/mkt-dev/src/boost_1_47_0_rc/boost/range/adaptor/map.hpp:14,
                 from /usr/local/mkt-dev/src/boost_1_47_0_rc/boost/range/adaptors.hpp:20,
                 from test2.cpp:4:
/usr/local/mkt-dev/src/boost_1_47_0_rc/boost/iterator/transform_iterator.hpp: In member function ‘typename boost::detail::transform_iterator_base<UnaryFunc, Iterator, Reference, Value>::type::reference boost::transform_iterator<UnaryFunction, Iterator, Reference, Value>::dereference() const [with UnaryFunc = boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<1> >, 0l> >, Iterator = boost::range_detail::integer_iterator<int>, Reference = boost::use_default, Value = boost::use_default, typename boost::detail::transform_iterator_base<UnaryFunc, Iterator, Reference, Value>::type::reference = int&]’:
/usr/local/mkt-dev/src/boost_1_47_0_rc/boost/iterator/iterator_facade.hpp:517:32:   instantiated from ‘static typename Facade::reference boost::iterator_core_access::dereference(const Facade&) [with Facade = boost::transform_iterator<boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<1> >, 0l> >, boost::range_detail::integer_iterator<int>, boost::use_default, boost::use_default>, typename Facade::reference = int&]’
/usr/local/mkt-dev/src/boost_1_47_0_rc/boost/iterator/iterator_facade.hpp:643:67:   instantiated from ‘reference boost::iterator_facade<I, V, TC, R, D>::operator*() const [with Derived = boost::transform_iterator<boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<1> >, 0l> >, boost::range_detail::integer_iterator<int>, boost::use_default, boost::use_default>, Value = int, CategoryOrTraversal = boost::detail::iterator_category_with_traversal<std::input_iterator_tag, boost::random_access_traversal_tag>, Reference = int&, Difference = long int, reference = int&]’
test2.cpp:13:70:   instantiated from here
/usr/local/mkt-dev/src/boost_1_47_0_rc/boost/iterator/transform_iterator.hpp:121:31: error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’

It seems that result_of<arg1(int)> returns int& instead of int.

[Nicolas Savoire <nicos@…>]

Ooops, I made a mistake, the failing example is:

#include <iostream>
#include <boost/range.hpp>
#include <boost/range/irange.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/phoenix.hpp>

using namespace boost::phoenix::arg_names;
using namespace boost::adaptors;

int main()
{
  std::cout << *boost::begin(boost::irange(0,5) | transformed( arg1 ));
}

[Thomas Heller]

It seems that result_of<arg1(int)> returns int& instead of int.

Good observation. This shouldn't be the case. The right return type is "int const &" in that case. I commit the necessary fix to trunk. And will ask the release managers to merge to release so the release won't suffer this defect. However, it is quite late in the release process, so chances are that it won't make it.

As a small workaround, I suggest the following:

boost::irange(0,5) | transformed( val( arg1 ) )

Thanks for your report.

[Nicolas Savoire <nicos@…>]

Thanks for the quick fix !

[Thomas Heller]

Replying to Nicolas Savoire <nicos@…>:

Thanks for the quick fix !

No problem. The tests on the release branch look good. The fix will be part of 1.47.0