[BOOST_FOREACH] Problem to iterate on a non-copyable container...
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_guardboost::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<int>::MyContainer(const MyContainer<int>&)
I also have :
error: no matching function for call to
‘MyContainer<int>::MyContainer(boost::foreach_detail_::rvalue_probe
The compiler complains about not having a copy constructor
That is because you are passing an rvalue to BOOST_FOREACH. All non-copyable containers must be passed as an lvalue. Paul -- View this message in context: http://boost.2283326.n4.nabble.com/BOOST-FOREACH-Problem-to-iterate-on-a-non... Sent from the Boost - Dev mailing list archive at Nabble.com.
On Tue, 19 May 2015 at 15:16 nico
Hi Nico, You can't do what you are trying to do in C++03. To accomplish it, you need C++11 move semantics to be able to move the MyContainer out of the Get function. Even without using BOOST_FOREACH, the following code fails; GetContainer<int> getter(v, m); MyContainer<int> c = getter.Get(); // <-- Error. Here's an example with the necessary changes; I changed the scoped_lock to a unique_lock and added a move constructor. 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) {} MyContainer(MyContainer&& other) : m_vector(other.m_vector) { m_lock = std::move(other.m_lock); other.m_vector = nullptr; } 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::unique_lockboost::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; }; Once you have move semantics though, you should have access to range-based-for, which is also C++11 for(auto&& i : getter.Get()) { std::cout << i << std::endl; } The above code works, so do you still need BOOST_FOREACH? -- chris
Hello Chris, and thank you for your reply. I'm feel like an old guy: I don't even ear about move semantic. I wish I'll be quickly able to work on a modern os and compiler... For my case, with the old C++, I finally made almost like you: change the lock to an unqiue lock, and provide a copy constructor: MyContainer(const MyContainer& other) : m_vector(other.m_vector), m_lock(*other.m_lock.mutex()) { } It's not a move semantic, but it did the job, and is usable with BOOST_FOREACH. But I have to change the mutex to a recursive_mutex... -- View this message in context: http://boost.2283326.n4.nabble.com/BOOST-FOREACH-Problem-to-iterate-on-a-non... Sent from the Boost - Dev mailing list archive at Nabble.com.
Actually, I think it would be better to default construct the lock on copy: MyContainer(const MyContainer& other) : m_vector(other.m_vector), m_lock() { } Because on copy you want to severe the relationship, so there is one lock associated with each copy of the document(or data). Paul -- View this message in context: http://boost.2283326.n4.nabble.com/BOOST-FOREACH-Problem-to-iterate-on-a-non... Sent from the Boost - Dev mailing list archive at Nabble.com.
participants (3)
-
Chris Glover -
nico -
pfultz2