c++ - Why is trying to store a pointer to function ambiguous -

here code:

    #include <functional>     #include <iostream>     #include<vector>      using namespace std;      // vector iterator     template <class t> class vit     {             private:             //vector<t>::iterator it;             vector<t> m_v;             function<bool (t, t)> m_fptr;             int len, pos;             public:             vit(vector<t> &v) { this->m_v = v; len = v.size(); pos = 0;};            //       it= v.begin(); };             bool next(t &i) {                     //if(it == m_v.end()) return false;                     if(pos==len) return false;                     //i = *it;                     = m_v[pos];                     //if(idle) { idle = false ; return true; }                     //it++;                     pos++;                     return true;};             //bool idle = true;             void set_same(function<bool (t,t)> fptr) { m_fptr = fptr ;};             //void set_same(function<bool(int, int)> fun) { return ; }             bool grp_begin() {                     return pos == 0 || ! m_fptr(m_v[pos], m_v[pos-1]); };             bool grp_end() {                     return pos == len || ! m_fptr(m_v[pos], m_v[pos+1]); };     };       bool is_same(int a, int b) { return == b; }      main()     {             vector<int>  v ={ 1, 1, 2, 2, 2, 3, 1, 1, 1 };             int total;             for(auto = v.begin(); != v.end(); it++) {                     if(it == v.begin() || *it != *(it-1)) {                             total = 0;                     }                      total += *it;                      if(it+1 == v.end() || *it != *(it+1)) {                             cout << total << endl;                     }             }              cout << "let's gry group" <<endl;             vit<int> g(v);             int i;             while(g.next(i)) { cout << << endl; }              cout << "now let's fancy" << endl;             vit<int> a_vit(v);             //auto is_same = [](int a, int b) { return == b; };             a_vit.set_same(is_same);             //int total;             while(a_vit.next(i)) {                     if(a_vit.grp_begin()) total = 0;                     total += i;                     if(a_vit.grp_end()) cout << total << endl ;             }     }         

when compile g++ -std=c++11 iter.cc -o iter, result:

    iter.cc: in function 'int main()':     iter.cc:63:17: error: reference 'is_same' ambiguous       a_vit.set_same(is_same);              ^     iter.cc:37:6: note: candidates are: bool is_same(int, int)      bool is_same(int a, int b) { return == b; }           ^     in file included /usr/include/c++/5.3.0/bits/move.h:57:0,                      /usr/include/c++/5.3.0/bits/stl_pair.h:59,                      /usr/include/c++/5.3.0/utility:70,                      /usr/include/c++/5.3.0/tuple:38,                      /usr/include/c++/5.3.0/functional:55,                      iter.cc:1:     /usr/include/c++/5.3.0/type_traits:958:12: note:                         template<class, class> struct std::is_same          struct is_same;                 ^ 

by way of explanation, have created class called 'vit'. 2 things: iterate on vector, , determine if new group has been reached.

the class function 'set_same' supposed store function provided calling class determine if 2 adjacent elements of vector in same group. however, can't seem store function in class future use grp_begin() , grp_end() on account of ostensible ambiguity of is_same.

what gives?

there is_same function defined , there struct is_same defined by c++ standard library. since using namespace std, compiler doesn't know is_same meant use.