Cannot create unordered_map of tuple<int, int, int>

Question

I'm using std::unordered_map<std::tuple<int, int, int>, float> . However, VS2010 will not compile the instantiation. I explicitly provided a hash specialization and an operator== overload. The error message refers to

std::unordered_map<NodeType, float> g_score;

And here is the full text of the error:

1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\tuple(127): error C2440: 'initializing' : cannot convert from 'const NodeType' to 'int'
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxtuple0(9) : see reference to function template instantiation 'std::tr1::_Cons_node<_Car,_Cdr>::_Cons_node<_Ty,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&>(_Farg0 &&,_Farg1,_Farg2,_Farg3,_Farg4,_Farg5,_Farg6,_Farg7,_Farg8,_Farg9)' being compiled
1>          with
1>          [
1>              _Car=int,
1>              _Cdr=std::tr1::_Cons_node<int,std::tr1::_Cons_node<int,std::tr1::_Tuple_type<std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil>::_Type>>,
1>              _Ty=NodeType,
1>              _Farg0=NodeType,
1>              _Farg1=std::tr1::_Nil &,
1>              _Farg2=std::tr1::_Nil &,
1>              _Farg3=std::tr1::_Nil &,
1>              _Farg4=std::tr1::_Nil &,
1>              _Farg5=std::tr1::_Nil &,
1>              _Farg6=std::tr1::_Nil &,
1>              _Farg7=std::tr1::_Nil &,
1>              _Farg8=std::tr1::_Nil &,
1>              _Farg9=std::tr1::_Nil &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\utility(145) : see reference to function template instantiation 'std::tr1::tuple<_Arg0,_Arg1,_Arg2>::tuple<const std::tr1::tuple<_Arg0,_Arg1,_Arg2>>(_Farg0 &&)' being compiled
1>          with
1>          [
1>              _Arg0=int,
1>              _Arg1=int,
1>              _Arg2=int,
1>              _Farg0=const std::tr1::tuple<int,int,int>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\utility(142) : while compiling class template member function 'std::_Pair_base<_Ty1,_Ty2>::_Pair_base(const std::tr1::tuple<_Arg0,_Arg1,_Arg2> &&,float &&)'
1>          with
1>          [
1>              _Ty1=const NodeType,
1>              _Ty2=float,
1>              _Arg0=int,
1>              _Arg1=int,
1>              _Arg2=int
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\utility(174) : see reference to class template instantiation 'std::_Pair_base<_Ty1,_Ty2>' being compiled
1>          with
1>          [
1>              _Ty1=const NodeType,
1>              _Ty2=float
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\unordered_map(279) : see reference to class template instantiation 'std::pair<_Ty1,_Ty2>' being compiled
1>          with
1>          [
1>              _Ty1=const NodeType,
1>              _Ty2=float
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\unordered_map(275) : while compiling class template member function 'float &std::tr1::unordered_map<_Kty,_Ty>::operator [](const std::tr1::tuple<_Arg0,_Arg1,_Arg2> &)'
1>          with
1>          [
1>              _Kty=NodeType,
1>              _Ty=float,
1>              _Arg0=int,
1>              _Arg1=int,
1>              _Arg2=int
1>          ]
1>          c:\repo\render\render\sim\simcontext.cpp(155) : see reference to class template instantiation 'std::tr1::unordered_map<_Kty,_Ty>' being compiled
1>          with
1>          [
1>              _Kty=NodeType,
1>              _Ty=float
1>          ]
1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\tuple(127): error C2439: 'std::tr1::_Cons_node<_Car,_Cdr>::_Value' : member could not be initialized
1>          with
1>          [
1>              _Car=int,
1>              _Cdr=std::tr1::_Cons_node<int,std::tr1::_Cons_node<int,std::tr1::_Tuple_type<std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil>::_Type>>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\tuple(170) : see declaration of 'std::tr1::_Cons_node<_Car,_Cdr>::_Value'
1>          with
1>          [
1>              _Car=int,
1>              _Cdr=std::tr1::_Cons_node<int,std::tr1::_Cons_node<int,std::tr1::_Tuple_type<std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil>::_Type>>
1>          ]

Uncertain where to proceed, as I've never seen this error before. Any suggestions?

Edit: Interestingly, the unordered_set<NodeType> right before this compiles cleanly.

Try this for an SSCCE:

#include <deque>
#include <tuple>
#include <unordered_map>
#include <unordered_set>

void GetPath() {
    typedef std::tuple<int, int, int> NodeType;
    struct node_hasher : public std::unary_function<const NodeType&, std::size_t> {
        std::size_t operator()(const NodeType& node) const {
            return std::hash<int>()(std::get<0>(node) + std::get<0>(node) + std::get<0>(node) + std::get<1>(node) + std::get<1>(node) + std::get<2>(node));
        }
    };
    std::unordered_set<NodeType, node_hasher> closed_set;
    std::unordered_map<NodeType, float, node_hasher> g_score;
    std::unordered_map<NodeType, float, node_hasher> f_score;
    std::unordered_map<NodeType, NodeType, node_hasher> came_from;
    auto node_comparator = [&](NodeType lhs, NodeType rhs) {
        return f_score[lhs] < f_score[rhs];
    };
}

int main() {
}

Fails to compile with the same error in the empty project. If you uncomment the node_comparator lambda, it works just fine. No wonder I had trouble with it- it's another VS bug.

Answer 1

This is a bug in the Visual C++ 2010 Standard Library. See the following report on Microsoft Connect:

C++ map<tuple<...>, V> compilation problems

The bug has been fixed for Visual Studio 11. Your example compiles without error using the Visual Studio 11 Beta.

Answer 2

Hint... implement hashing and equality as lambdas, then use the type of these lambdas as template parameters:

auto h = [](const TKey& x) { ... };
auto eq = [](const TKey& x, const TKey& y) { ... };

std::unordered_map<TKey, TValue, decltype(h), decltype(eq)> m;

Answer 3

Try moving NodeType and node_hasher to namespace scope. In C++03 local types can't be used as template arguments. Maybe VS2010 simply hasn't implemented that change yet. I'm simply guessing. I don't have VS2010 and thus haven't tried this experiment with your SSCCE.