I have a question about a particular problem I'm having with boost::lambda. I've distilled it down to a tiny complete app (shown below). The complier is complaining about bl::_1 is a const std::string, but &Map::value_type::second is a member_data_pointer to a non-const string. This line compiles with boost 1.42, but not in 1.46 (using MSVC 2008). I have two questions: 1) is the line of code in question actually valid? I.e. is this a boost::lambda bug or is this my bug? 2) If it is my bug, then to fix the code I need to coerce [&Map::value_type::second] to a CONST - problem is that the only way I can figure out is to use an ugly const_cast<>. Is there a cleaner way to do this? Source code follows: ------------------------------------------------------------------------------------------------------------ #include <iostream> #include <string> #include <map> #include <cassert> #include <boost/assign.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> namespace bl = boost::lambda; int main() { // create two simple maps and populate them typedef std::map<long, std::string> Map; Map m = boost::assign::map_list_of(0, "hello ")(1, "world!"); // non-const map Map const cm = boost::assign::map_list_of(0, "hello ")(1, "world!"); // const map // this works: // concatenate the std::string parts of the non-const map and send to std::cout // std::string output; std::for_each( m.begin(), m.end(), output += bl::bind(&Map::value_type::second, bl::_1)); std::cout << output << std::endl; assert(output == "hello world!"); // works with boost 1.42, however it fails to compile with boost 1.46 // concatenate the std::string parts of the const map and send to std::cout // output.clear(); std::for_each( cm.begin(), cm.end(), output += bl::bind(&Map::value_type::second, bl::_1)); // <---- COMPILER ERROR HERE WITH BOOST 1.46 std::cout << output << std::endl; assert(output == "hello world!"); // this compiles, but uses an ugly const_cast<> // concatenate the std::string parts of the const map and send to std::cout // output.clear(); std::for_each( cm.begin(), cm.end(), output += bl::bind(const_cast<std::string const Map::value_type::*>(&Map::value_type::second), bl::_1)); // <---- UGLY std::cout << output << std::endl; assert(output == "hello world!"); return 0; }