id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
5408,fold(transform(.... )) gives erroneous result: dangling reference?,joe@…,Joel de Guzman,"The code below demonstrates a problem using fusion's transform on a fold view in conjunction with a phoenix functional. It produces the output:

   Should be the same: 1 =? 4.59177e-41

it should produce

   Should be the same: 1 =? 1

Thanks,
Joe


{{{
#include <iostream>
#include <cmath>
#include <boost/detail/lightweight_test.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_function.hpp>
#include <boost/fusion/container.hpp>
#include <boost/fusion/functional.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/fusion/include/fold.hpp>
#include <boost/fusion/include/transform.hpp>
#include <boost/type_traits.hpp>
#include <boost/mpl/assert.hpp>

using namespace boost::fusion;
using namespace boost::phoenix;

typedef float OutputType;

// A general error function, measuring the difference between two output patterns.
struct error_function3 {
	template <typename Outputs1, typename Outputs2>
	struct result
	{
		typedef OutputType type;
	};

	template <typename Outputs1, typename Outputs2>
	OutputType operator()(Outputs1& outputs1, Outputs2& outputs2) const
	{
		using boost::phoenix::arg_names::_1;
		using boost::phoenix::arg_names::_2;
		using boost::fusion::fold;
		using boost::fusion::transform;

		float bad_result = fold(transform(outputs1, outputs2, (_1 - _2) * (_1 - _2)), 0, _1 + _2);
		float good_result = fold(as_vector(transform(outputs1, outputs2, (_1 - _2) * (_1 - _2))), 0, _1 + _2);

		std::cout << ""Should be the same: "" << good_result << "" =? "" << bad_result << std::endl;
		return good_result;
	}
};

int main() {
	using boost::phoenix::arg_names::_1;
	using boost::phoenix::arg_names::_2;
	vector<OutputType, OutputType> o1 = make_vector(1., 2.);
	vector<OutputType, OutputType> o2 = make_vector(2., 3.);

	boost::phoenix::function<error_function3> const error;
	std::cout << error(_1, _2)(o1, o2) << std::endl;
}
}}}
",Bugs,closed,To Be Determined,fusion,Boost 1.47.0,Problem,wontfix,,joel@…