calling map::insert through bind.
Hi list. I've got a question on calling map::insert using bind. What I'd like to do is to copy all members in m into m2: #include <iostream> #include <algorithm> #include <map> #include <utility> #include <boost/lambda/algorithm.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> using namespace std; using namespace boost::lambda; int main() { map<string, int> m; map<string, int> m2; m["a"] = 1; m["b"] = 2; m2["c"] = 3; for_each(m.begin(), m.end(), bind(&map<string, int>::insert, &m2, bind(&make_pair, bind(&map<string, int>::value_type::first, _1), bind(&map<string, int>::value_type::second, _1)))); return EXIT_SUCCESS; } Unfortunately, the above code fails to compile and I have no idea why it fails. I'm using g++ and the errors are as follows: g++ map_test.cpp map_test.cpp: In function 'int main()': map_test.cpp:26: error: no matching function for call to 'bind(<unknown type>, const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<2, boost::lambda::function_action<2, boost::lambda::detail::unspecified> >, boost::tuples::tuple<const std::basic_string<char, std::char_traits<char>, std::allocator<char> > std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::* const, const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<2, boost::lambda::function_action<2, boost::lambda::detail::unspecified> >, boost::tuples::tuple<int std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::* const, const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >)' Any idea on this? Sincerely, Minkoo Seo -- View this message in context: http://www.nabble.com/calling-map%3A%3Ainsert-through-bind.-tf2150829.html#a... Sent from the Boost - Users forum at Nabble.com.
On 8/23/06, Minkoo Seo <minkoo.seo@gmail.com> wrote:
for_each(m.begin(), m.end(), bind(&map<string, int>::insert, &m2, bind(&make_pair, bind(&map<string, int>::value_type::first, _1), bind(&map<string, int>::value_type::second, _1))));
Unfortunately, the above code fails to compile and I have no idea why it fails. I'm using g++ and the errors are as follows:
First off, just thought I would mention that for an example such as this, regular boost::bind would probably suffice. You don't need lambda. Second of all, I don't know which insert function you are trying to call, but you should be able to write this code instead, which is much simpler: for_each(m.begin(), m.end(), bind(&map<string, int>::insert, m2, _1)); Finally, even that fails to compile! I believe the problem is that since insert is an overloaded function, boost cannot figure out which one to call. So you help it out by type-casting explicitly, like this: typedef pair<map<string, int>::iterator, bool> (map<string, int>::* InsertFunc)(const map<string, int>::value_type&); for_each(m.begin(), m.end(), bind(static_cast<InsertFunc>(&map<string, int>::insert), m2, _1)); It's ugly, but it works (actually, I tried with lambda and it still didn't work, but with regular boost::bind it does). Now after going to ALL that work just so you can use for_each, don't you just want to forget it and use iterators? for( map<string, int>::const_iterator it = m.begin(); it != m.end(); ++it ) m2.insert(*it); Phillip Hellewell
On 8/23/06, Phillip Hellewell <sshock@gmail.com> wrote:
[snipped]
Now after going to ALL that work just so you can use for_each, don't you just want to forget it and use iterators?
for( map<string, int>::const_iterator it = m.begin(); it != m.end(); ++it ) m2.insert(*it);
And after ALL this, you could write just: std::map<std::string, int> m2(m1); What am I missing? maps are copy-constructible!
Phillip Hellewell
-- Felipe Magno de Almeida
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Felipe Magno de Almeida -
Minkoo Seo -
Phillip Hellewell