Boost d_ary_heap/priority_queue compile error: deleted function - c++

Question

I am using a Dijkstra for finding a shortest path in graph. I used to use std::set but I think a heap could perform better. But I am having troubles using the d_ary_heap or the priority_queue.
This is a simplified version:
#include <string>
#include <inttypes.h> // for uint32_t
#include <boost/heap/fibonacci_heap.hpp>
#include <boost/heap/binomial_heap.hpp>
#include <boost/heap/d_ary_heap.hpp>
#include <boost/heap/priority_queue.hpp>
using namespace std;
struct __attribute__ ((__packed__)) __attribute__((aligned(8)) Cmp {
// Do *not* reorder the following two fields or comparison will break.
const int32_t _id;
const float _cost;
Cmp(int32_t id, float cost) : _id(id), _cost(cost) {
}
};
struct Entry {
Cmp _cmp;
string str = "some variable";
Entry(int32_t id, float cost) : _cmp(id, cost) {}
Entry(Entry &&e) : _cmp(e._cmp._id, e._cmp._cost) {}
Entry(const Entry &e) : _cmp(e._cmp._id, e._cmp._cost) {}
};
template<class T>
struct gt_entry: public binary_function <T, T, bool>
{
bool operator()(const T &l, const T &r) const
{
return *(int64_t const *)&l > *(int64_t const *)&r;
}
};
typedef boost::heap::d_ary_heap<
Entry,
boost::heap::arity<2>,
boost::heap::compare<gt_entry<Entry> > > DHeap;
typedef boost::heap::binomial_heap<
Entry,
boost::heap::compare<gt_entry<Entry> > > BHeap;
typedef boost::heap::fibonacci_heap<
Entry,
boost::heap::compare<gt_entry<Entry> > > FHeap;
typedef boost::heap::priority_queue<
Entry,
boost::heap::compare<gt_entry<Entry> > > PQueue;
int main() {
//DHeap h; // Doesn't compile
//PQueue h; // Doesn't compile
//BHeap h; // Works but slower than FHeap
FHeap h; // Works but only 3% performance increase vs std::set
h.push(Entry(1, 500.1));
h.top();
h.pop();
return 0;
}
(I am using the packaging of the _cost and _id to speed up comparison, see C++ Optimize if/else condition if you are interested.)
This seems to be the relevant error line, I guess it has something to do with the move or copy constructor.
.../move.h:177:7: error: use of deleted function ‘Entry& Entry::operator=(const Entry&)’
heaps.cpp:19:8: note: ‘Entry& Entry::operator=(const Entry&)’ is implicitly declared as deleted because ‘Entry’ declares a move constructor or move assignment operator
I am using gcc 4.6 (-std=c++0x) and boost 1.50.

Answer 1

Your gcc version does not implement the rules for implicitly deleted functions correctly. The code works at least with gcc 4.7.
A quick workaround is to declare the move assignment operator Entry& operator=(Entry&&) as well.
In general I wouldn't recommend using C++11 with a compiler that is not completely up-to-date.
Also: You move constructor and copy constructor behave odd. They don't copy/move the string. You might want to change that. If you really only need one string across, make it a static member.