#include <map>
#include <set>
#include <iostream>

using namespace std;

// work - for let say - sets
template <class Type_>
struct Key { 
   Key(typename Type_::const_iterator it) : value(*it) {}
   typename Type_::key_type value;
};

// work - for map<***>
template <class Key_, class Value_, class Comp_, class Alloc_>
struct Key<map<Key_, Value_,Comp_,Alloc_> > { 
   typedef map<Key_, Value_,Comp_,Alloc_> Type_;
   Key(typename Type_::const_iterator it) : value(it->first) {}
   typename Type_::key_type value;
};


template< typename T >
const typename T::key_type getKey( const typename T::const_iterator& it )
{
    return Key<T>(it).value;
}

template< typename T >
void dumpOut( T& coll )
{
    for ( typename T::const_iterator it = coll.begin(); it != coll.end(); ++it )
    {
        const typename T::key_type& a = getKey<T>(it);
        cout << a << endl;
    }
}

int main()
{
    set<int> s1;
    s1.insert(10);
    s1.insert(15);
    s1.insert(20);

    dumpOut< set<int> >( s1 );

    map<int, int> m1;
    m1.insert( pair<int, int>(11, -1) );
    m1.insert( pair<int, int>(16, -1) );
    m1.insert( pair<int, int>(21, -1) );

    dumpOut< map<int, int> >( m1 );

    return 0;
}