Using boost::multi_index_container - c++

Question

I've been attempting to use boost::multi_index_container to solve a problem I'm having. However, the multi_index_container fails to compile even the declaration. The error is deep in an MPL function and I have little idea where the fault lies.
boost::multi_index_container<
NodeType,
boost::multi_index::indexed_by<
boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>, decltype(node_comparator)>,
boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>
>
> open_set(
boost::make_tuple(node_comparator)
);
In this case, node_comparator is a lambda, and NodeType itself already has a std::hash specialization. Here's the text of the error:
1>d:\backups\code\boost_1_47_0\boost\multi_index\detail\node_type.hpp(56): error C2903: 'node_class' : symbol is neither a class template nor a function template
1> d:\backups\code\boost_1_47_0\boost\mpl\aux_\preprocessed\plain\apply_wrap.hpp(49) : see reference to class template instantiation 'boost::multi_index::detail::index_node_applier::apply<IndexSpecifierIterator,Super>' being compiled
1> with
1> [
1> IndexSpecifierIterator=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>,
1> Super=boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>>
1> ]
1> d:\backups\code\boost_1_47_0\boost\mpl\aux_\preprocessed\plain\bind.hpp(207) : see reference to class template instantiation 'boost::mpl::apply_wrap2<F,T1,T2>' being compiled
1> with
1> [
1> F=boost::multi_index::detail::index_node_applier,
1> T1=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>,
1> T2=boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>>
1> ]
1> d:\backups\code\boost_1_47_0\boost\mpl\aux_\preprocessed\plain\apply_wrap.hpp(49) : see reference to class template instantiation 'boost::mpl::bind2<F,T1,T2>::apply<U1,U2>' being compiled
1> with
1> [
1> F=boost::multi_index::detail::index_node_applier,
1> T1=boost::mpl::_2,
1> T2=boost::mpl::_1,
1> U1=boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>>,
1> U2=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>
1> ]
1> d:\backups\code\boost_1_47_0\boost\mpl\aux_\preprocessed\plain\apply.hpp(63) : see reference to class template instantiation 'boost::mpl::apply_wrap2<F,T1,T2>' being compiled
1> with
1> [
1> F=boost::mpl::bind2<boost::multi_index::detail::index_node_applier,boost::mpl::_2,boost::mpl::_1>,
1> T1=boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>>,
1> T2=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>
1> ]
1> d:\backups\code\boost_1_47_0\boost\mpl\aux_\preprocessed\plain\reverse_iter_fold_impl.hpp(82) : see reference to class template instantiation 'boost::mpl::apply2<F,T1,T2>' being compiled
1> with
1> [
1> F=boost::mpl::bind2<boost::multi_index::detail::index_node_applier,boost::mpl::_2,boost::mpl::_1>,
1> T1=boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>>,
1> T2=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>
1> ]
1> d:\backups\code\boost_1_47_0\boost\mpl\reverse_iter_fold.hpp(43) : see reference to class template instantiation 'boost::mpl::aux::reverse_iter_fold_impl<N,First,Last,State,BackwardOp,ForwardOp>' being compiled
1> with
1> [
1> N=2,
1> First=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,0>,
1> Last=boost::mpl::v_iter<boost::mpl::vector2<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,2>,
1> State=boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>,
1> BackwardOp=boost::mpl::bind2<boost::multi_index::detail::index_node_applier,boost::mpl::_2,boost::mpl::_1>,
1> ForwardOp=boost::mpl::protect<boost::mpl::arg<1>>
1> ]
1> d:\backups\code\boost_1_47_0\boost\multi_index\detail\node_type.hpp(70) : see reference to class template instantiation 'boost::mpl::reverse_iter_fold<Sequence,State,BackwardOp>' being compiled
1> with
1> [
1> Sequence=boost::multi_index::indexed_by<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,
1> State=boost::multi_index::detail::index_node_base<NodeType,std::allocator<NodeType>>,
1> BackwardOp=boost::mpl::bind2<boost::multi_index::detail::index_node_applier,boost::mpl::_2,boost::mpl::_1>
1> ]
1> d:\backups\code\boost_1_47_0\boost\multi_index_container.hpp(75) : see reference to class template instantiation 'boost::multi_index::detail::multi_index_node_type<Value,IndexSpecifierList,Allocator>' being compiled
1> with
1> [
1> Value=NodeType,
1> IndexSpecifierList=boost::multi_index::indexed_by<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>,
1> Allocator=std::allocator<NodeType>
1> ]
1> c:\repo\render\render\sim\simcontext.cpp(264) : see reference to class template instantiation 'boost::multi_index::multi_index_container<Value,IndexSpecifierList>' being compiled
1> with
1> [
1> Value=NodeType,
1> IndexSpecifierList=boost::multi_index::indexed_by<boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>,Wide::Sim::`anonymous-namespace'::<lambda8>>,boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>>
1> ]
Any suggestions as to the cause?
Edit: There's pretty much no context to be had. But here's an SSCCE for those of you who can't live without one:
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/hashed_index.hpp>
struct NodeType {
int x, y, z;
float g_score;
NodeType(int ax, int ay, int az) {
x = ax;
y = ay;
z = az;
}
NodeType() {}
bool operator==(const NodeType& other) const {
return x == other.x && y == other.y && z == other.z;
}
};
template<> struct std::hash<NodeType> : public std::unary_function<const NodeType&, std::size_t> {
std::size_t operator()(const NodeType& node) const {
return std::hash<int>()(node.x * 100000 + node.y * 1000 + node.z);
}
};
template<> struct boost::hash<NodeType> : public std::unary_function<const NodeType&, std::size_t> {
std::size_t operator()(const NodeType& node) const {
return std::hash<int>()(node.x * 100000 + node.y * 1000 + node.z);
}
};
int main() {
auto h = [&](NodeType x) {
return 5.0f; // details irrelevant
};
auto node_comparator = [&](NodeType lhs, NodeType rhs) {
return lhs.g_score + h(lhs) < rhs.g_score + h(rhs);
};
boost::multi_index_container<
NodeType,
boost::multi_index::indexed_by<
boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>, decltype(node_comparator)>,
boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>
>
> open_set(
boost::make_tuple(node_comparator)
);
}

Answer 1

After your SSCCE post: maybe you forgot to add the following?
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/identity.hpp>
Other than that, I can't compile your code here because my environment is pre-C++11, but I did manage to make it work adding the missing includes and replacing lambdas with regular named functions. Note I had to change the construction args of open_setas explained in another answer:
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/identity.hpp>
struct NodeType {
int x, y, z;
float g_score;
NodeType(int ax, int ay, int az) {
x = ax;
y = ay;
z = az;
}
NodeType() {}
bool operator==(const NodeType& other) const {
return x == other.x && y == other.y && z == other.z;
}
};
template<> struct boost::hash<NodeType> : public std::unary_function<const NodeType&, std::size_t> {
std::size_t operator()(const NodeType& node) const {
return boost::hash<int>()(node.x * 100000 + node.y * 1000 + node.z);
}
};
double h(NodeType x) {
return 5.0f;
}
bool node_comparator(NodeType lhs, NodeType rhs) {
return lhs.g_score + h(lhs) < rhs.g_score + h(rhs);
}
int main() {
typedef boost::multi_index_container<
NodeType,
boost::multi_index::indexed_by<
boost::multi_index::ordered_non_unique<boost::multi_index::identity<NodeType>, bool (*)(NodeType,NodeType)>,
boost::multi_index::hashed_unique<boost::multi_index::identity<NodeType>>
>
> open_set_t;
open_set_t open_set(
boost::make_tuple(
boost::make_tuple(
boost::multi_index::identity<NodeType>(),
&node_comparator
),
open_set_t::nth_index<1>::type::ctor_args()
)
);
}
Additional note: your lambda functions are taking NodeTypes by value, I guess they'd be more efficient if they accepted their arguments as const NodeType&s.

Answer 2

Trying to guess what the problem is with so little context makes for a fun pastime but reduces your chances that you get a useful answer. Ideally you should be providing a complete testcase (i.e. a short compilable program) showing the issue. Anyway, a shot in the dark: you say that NodeTypehas a dedicated std::hash specialization, but Boost.MultiIndex uses boost::hash as its default hash generator. Try looking there.

Answer 3

Another shot in the dark (i think this is it): as decltype(node_comparator) is not default constructible you have to provide an initialization value (node_comparator itself) during open_setconstruction. This is what seemingly you're trying to do, but incorrectly: the right way is as follows (modulo potential typos, more details here):
typedef boost::multi_index_container<
NodeType,
...
> open_set_t;
open_set_t open_set(
boost::make_tuple(
boost::make_tuple(
boost::multi_index::identity<NodeType>(),
node_comparator
),
open_set_t::nth_index<1>::type::ctor_args()
)
);
Given the verbosity imposed by the use of a lambda expression here, I think you're better off by writing a used-defined, default constructible comparator class instead of node_comparator.