Question

I recently ran into a problem that I thought boost::lambda or boost::phoenix could help be solve, but I was not able to get the syntax right and so I did it another way. What I wanted to do was remove all the elements in ‘strings’ that were less than a certain length and not in another container.

This is my first try:

std::vector<std::string> strings = getstrings(); std::set<std::string> others = getothers(); strings.erase(std::remove_if(strings.begin(), strings.end(), (_1.length() < 24 &&  others.find(_1) == others.end())), strings.end()); 

How I ended up doing it was this:

struct Discard {     bool operator()(std::set<std::string> &cont, const std::string &s)     {         return cont.find(s) == cont.end() && s.length() < 24;     } };  lines.erase(std::remove_if( lines.begin(), lines.end(), boost::bind<bool>(Discard(), old_samples, _1)), lines.end()); 

Answer 1

You need boost::labmda::bind to lambda-ify function calls, for example the length < 24 part becomes:

bind(&string::length, _1) < 24 

EDIT

See ‘Head Geek”s post for why set::find is tricky. He got it to resolve the correct set::find overload (so I copied that part), but he missed an essential boost::ref() — which is why the comparison with end() always failed (the container was copied).

int main() {   vector<string> strings = getstrings();   set<string> others = getothers();   set<string>::const_iterator (set<string>::*findFn)(const std::string&) const = &set<string>::find;   strings.erase(     remove_if(strings.begin(), strings.end(),         bind(&string::length, _1) < 24 &&         bind(findFn, boost::ref(others), _1) == others.end()       ), strings.end());   copy(strings.begin(), strings.end(), ostream_iterator<string>(cout, ', '));   return 0; }