std::copy to std::cout for std::pair

Question

I have next code:

#include 
#include 
#include 

Answer 1

Just passing by, but this did the job for me, so it can for somebody else (cut version):

template
struct first_of {
    First& operator()(std::pair& v) const {
        return v.first;
    }
};

Use case given:

transform (v.begin (), v.end (), 
           ostream_iterator(cout, "\n"), first_of ());