[boost-users] [assign] std::vector initialisation by boost::assign::list_of
The code is compilable on msvc but is not on gcc-4.3: #include <boost/assign/list_of.hpp> #include <vector> int main() { //OK std::vector<int> v = boost::assign::list_of(1)(2); // error std::vector<int> v(boost::assign::list_of(1)(2)); return 0; } I can initialise std::vector in a first way. But the problem occurs when i try to initialise std::vector in a class initialization list: class sss { std::vector<int> v; sss() : v(boost::assign::list_of(1)(2)) {} }; -- Regards, Andrey
Looks like gcc is not smart enough to guess to call `operator std::vector<int>()` ..\example\ddd.cpp:12: error: call of overloaded 'vector(boost::assign_detail::generic_list<int>&)' is ambiguous ... stl_vector.h:241: note: candidates are: std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = int, _Alloc = std::allocator<int>] ... stl_vector.h:227: note: std::vector<_Tp, _Alloc>::vector(size_t, const _Tp&, const _Alloc&) [with _Tp = int, _Alloc = std::allocator<int>] ... stl_vector.h:215: note: std::vector<_Tp, _Alloc>::vector(const _Alloc&) [with _Tp = int, _Alloc = std::allocator<int>] -- Regards, Andrey
On Wed, Mar 17, 2010 at 1:32 PM, Andrey Torba <andreytorba@gmail.com> wrote:
list_of implements 2 members: implicit conversion opertor to the container type and the to_adapter member. You can cast list_of instance to your vector<int> if that with adapter does not work. Other solution can be: If you need efficiency, you still can use the vector ctor which reserves the number of items in a vector and than copies the elements from the list. sss() : v(2) { v = list_of...; } Regards, Ovanes
Actually I tested some of them with gcc and the only solution I came up to resolve ambiguity is: #include <boost/assign.hpp> #include <vector> #include <iterator> #include <algorithm> #include <iostream> using namespace std; using namespace boost; using namespace boost::assign; int main(int argc, char* argv[]) { typedef vector<int> int_vec; int_vec v = list_of(1)(2); int_vec v2(2); v2=list_of(1)(2).to_container(v2); ostream_iterator<int> oiter(cout, ","); copy(v2.begin(), v2.end(), oiter); } Hope that helps, Ovanes On Wed, Mar 17, 2010 at 1:52 PM, Ovanes Markarian <om_boost@keywallet.com>wrote:
mmmm... Actually, I would probably create an empty vector and use the list_of in the constructor's body. Another idea I just came up with, is to use an transforming iterator, which iterates over the list_of instance and additionally can be compared with a default constructed iterator instance. Smth like: vector<int> v(my_iterator(list_of(1)(2)), my_iterator()); Regards, Ovanes On Wed, Mar 17, 2010 at 4:16 PM, Ovanes Markarian <om_boost@keywallet.com>wrote:
On 17 March 2010 17:58, Ovanes Markarian <om_boost@keywallet.com> wrote:
vector<int> v(my_iterator(list_of(1)(2)), my_iterator());
I think that result of `list_of` will be destroyed after `my_iterator(...)` call, so `my_iterator` will not be valid. -- Regards, Andrey
Hi Andrey, you can pass list by value. Compiler should be smart enough to eliminate the temporary. On the other hand, if you vector is always constant consider using a fusion vector. You can also introduce a helper function, which fills the vector with the desired list and returns it: struct sss { sss() : v(vector_items) {} private: // this function should be inlined with temporary elimination static vector<int> vector_items() { vector<int> v = list_of...; return v; } }; Hope that helps, Ovanes On Wed, Mar 17, 2010 at 8:30 PM, Andrey Torba <andreytorba@gmail.com> wrote:
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