Question

Searching in the second value of a map i use somthing like the following:

typedef std::map<int, int> CMyList;
static CMyList myList;

template<class t> struct second_equal
{
    typename typedef t::mapped_type mapped_type;
    typename typedef t::value_type value_type;

    second_equal(mapped_type f) : v(f)   {};
    bool operator()(const value_type &a) { return a.second == v;};

    mapped_type v;
};
...    
int i = 7;
CMyList::iterator it = std::find_if(myList.begin(), myList.end(), 
                                    second_equal<CMyList>(i));

Question: How can i do such a find in a single line without supplying a self written template?

Answer 1

Use a selector to select the first or the second element from the value_type that you get from the map.
Use a binder to bind the value (i) to one of the arguments of the std::equal_to function.
Use a composer to use the output of the selector as the other argument of the equal_to function.

//stl version
CMyList::iterator it = std::find_if(
    myList.begin(), 
    myList.end(), 
    std::compose1(
        std::bind2nd(equal_to<CMyList::mapped_type>(), i), 
        std::select2nd<CMyList::value_type>())) ;

//Boost.Lambda or Boost.Bind version
CMyList::iterator it = std::find_if(
    myList.begin(), 
    myList.end(), 
    bind( &CMyList::mapped_type::second, _1)==i);