On 09/03/2007 07:46 PM, Andreas Klöckner wrote:

Hi all,

I came up with the following implementation of a "flatten" operation that turns a sequence of sequences into a flat list:

[...]

It compiles (using gcc 4.2.1), but prints 0 instead of the expected 7. What am I doing wrong?

I'm not sure of what you might be doing wrong, but if you take away the lambda expression, and use another level of indirection things work for me: ----- cut ------ #include <iostream> #include #include #include #include #include #include #include #include // joins two sequences struct join { template struct apply { typedef typename boost::mpl::copy< Seq2, boost::mpl::back_inserter<Seq1> >::type type; }; }; template<class Sequence> struct flatten { typedef typename boost::mpl::fold< Sequence, typename boost::mpl::clear<Sequence>::type, join >::type type; }; typedef flatten< boost::mpl::vector< boost::mpl::vector_c, boost::mpl::vector_c > >::type flatvec; int main() { std::cout << boost::mpl::size<flatvec>::value << std::endl; } ----- cut ------ I hope it helps... Did you manage to fix this some other way? Cheers, Tiago -- Tiago de Paula Peixoto