Initialization of a templated data member cryptic error - c++

Question

This is my tmp.hpp:
#include <cstdlib>
#include <utility>
#include <unordered_map>
using namespace std;
struct int_int_hasher {
size_t operator()(pair<int, int> const& p) const {
return static_cast<size_t>(p.first) << 32 | p.second;
}
};
template<class T, class H>
class BiBag {
unordered_map<T, uint, H> t_to_id_;
};
And simple tmp.cpp:
#include "tmp.hpp"
class tmp {
BiBag<pair<int, int>, int_int_hasher> tt =
BiBag<std::pair<int, int>, int_int_hasher>();
};
The error message is beyond my understanding:
g++ -std=c++11 -O2 tmp.cpp -lm -o tmp
tmp.cpp:6:32: error: expected ‘;’ at end of member declaration
BiBag<std::pair<int, int>, int_int_hasher>();
^
tmp.cpp:6:32: error: declaration of ‘BiBag<std::pair<int, int>, int_int_hasher> tmp::int_int_hasher’ [-fpermissive]
In file included from tmp.cpp:2:0:
tmp.hpp:7:8: error: changes meaning of ‘int_int_hasher’ from ‘struct int_int_hasher’ [-fpermissive]
struct int_int_hasher {
^
tmp.cpp:6:46: error: expected unqualified-id before ‘>’ token
BiBag<std::pair<int, int>, int_int_hasher>();
^
tmp.cpp:6:16: error: wrong number of template arguments (1, should be 2)
BiBag<std::pair<int, int>, int_int_hasher>();
^
If I remove the hasher from the picture and replace the map with a simple <int,int> map I get no error.
Thank you.