I'm not sure of the title, because I'm not sure the issue comes from the "copyablility" of my container. I tryied quite everything but I can't get rid of this error.
Here is a simplified version of my code (please do not challenge the class design, I really would like to keep the end-used syntax in the BOOST_FOREACH):
template <typename T>
class MyContainer
{
public:
typedef typename std::vector<T>::iterator iterator;
typedef typename std::vector<T>::const_iterator const_iterator;
MyContainer(std::vector<T>& vec, boost::mutex& mutex) :
m_vector(vec),
m_lock(mutex)
{
}
iterator begin() { return m_vector.begin(); }
const_iterator begin() const { return m_vector.begin(); }
iterator end() { return m_vector.end(); }
const_iterator end() const { return m_vector.end(); }
private:
std::vector<T>& m_vector;
boost::lock_guard<boost::mutex> m_lock;
};
template <typename T>
struct GetContainer
{
GetContainer(std::vector<T>& vec, boost::mutex& mutex) :
m_vector(vec),
m_mutex(mutex)
{
}
MyContainer<T> Get()
{
return MyContainer<T>(m_vector, m_mutex);
}
std::vector<T>& m_vector;
boost::mutex& m_mutex;
};
int main()
{
std::vector<int> v;
v.push_back(1);
v.push_back(2);
boost::mutex m;
GetContainer<int> getter(v, m);
BOOST_FOREACH(int i, getter.Get())
{
std::cout << i << std::endl;
}
return 0;
}
The compiler complains about not having a copy constructor for MyContainer::MyContainer(const MyContainer&). I also have : error: no matching function for call to ‘MyContainer::MyContainer(boost::foreach_detail_::rvalue_probe >::value_type)’
I follow the extensibility tips: http://www.boost.org/doc/libs/1_58_0/doc/html/foreach/extensibility.html#foreach.extensibility.making__literal_boost_foreach__literal__work_with_non_copyable_sequence_types
But, making
MyContainer<T> : private boost::noncopyable
doesn't solve the issue. Nor defining the function
boost_foreach_is_noncopyable
or specializing the template struct
is_noncopyable
for MyContainer (in fact, how would I specialize this template for a template type ?)
Last "tip": If I remove the mutex and the lock from everywhere (I just pass the vector to GetContainer and to MyContainer), it works. But it doesn't work if I make
MyContainer<T> : private boost::noncopyable
(I expected it should, so I'm not sure my problem is with BOOST_FOREACH, but maybe because I return a copy of MyContainer with my getter ?)
I thank you if you read me until here, and thanks in advance for help.
Seems to be a limitation of BOOST_FOREACH with move-only types. I didn't find a way around it¹ (except for the - ugly - obvious approach to put the lock_guard
in a shared_ptr
).
You didn't specify a c++03 requirement, though, so you can make it work without BOOST_FOREACH by replacing lock_guard
with unique_lock
.
Here's my take on things in c++11 (note how generic it is):
#include <boost/thread.hpp>
#include <boost/range.hpp>
namespace detail {
template <typename R, typename M>
struct RangeLock {
RangeLock(R&r, M& m) : _r(r), _l(m) {}
RangeLock(RangeLock&&) = default;
using iterator = typename boost::range_iterator<R>::type;
iterator begin() { using std::begin; return begin(_r); }
iterator end () { using std::end; return end (_r); }
using const_iterator = typename boost::range_iterator<R const>::type;
const_iterator begin() const { using std::begin; return begin(_r); }
const_iterator end () const { using std::end; return end (_r); }
private:
R& _r;
boost::unique_lock<M> _l;
};
}
template <typename R, typename M>
detail::RangeLock<R,M> make_range_lock(R& r, M& mx) { return {r,mx}; }
template <typename R, typename M>
detail::RangeLock<R const,M> make_range_lock(R const& r, M& mx) { return {r,mx}; }
#include <vector>
#include <map>
int main() {
boost::mutex mx;
std::vector<int> const vec { 1, 2 };
std::map<int, std::string> const map { { 1, "one" }, { 2, "two" } };
for(int i : make_range_lock(vec, mx))
std::cout << i << std::endl;
for(auto& p : make_range_lock(map, mx))
std::cout << p.second << std::endl;
for(auto& p : make_range_lock(boost::make_iterator_range(map.equal_range(1)), mx))
std::cout << p.second << std::endl;
}
Prints
1
2
one
two
one
¹ not even using all the approaches from Using BOOST_FOREACH with a constant intrusive list