c++ - Why do we need a move constructor for vector of unique_ptr? -

it seems vc11 update 2, requires move constructor when pushing unique_ptr's in std::vector. documented behavior or known bug?

#include < iostream> #include <memory> #include <vector> struct test {     std::unique_ptr<int> m_l;     test(         std::unique_ptr<int>&& l)     {         m_l = std::move(l);     };     //move contructor test     test(test&& o)     {         m_l = std::move(o.m_l);     } }; void bar() {     std::vector<test> vec;     std::unique_ptr<int> a(new int);     //compiles fine without move constructor     test(std::move(a));     //requires move contructor compile     vec.push_back(         test(std::move(a))); } int main() {            bar();     return 0; }  

note

i tried above code sans move constructor on ideone c++11 , compiles fine.

you shouldn't have write move constructor yourself; should automatically generated compiler in case. however, vc11 doesn't implement functionality , iirc isn't going added until vs2013.

note vc11 complaining because presence of std::unique_ptr data member causes copy constructor deleted. §12.8p11 describes process of deleting class's copy constructor:

an implicitly-declared copy/move constructor inline public member of class. a defaulted copy/move constructor class x defined deleted (8.4.3) if x has:

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— a non-static data member of class type m (or array thereof) cannot copied/moved because overload resolution (13.3), applied m’s corresponding constructor, results in ambiguity or a function deleted or inaccessible defaulted constructor,

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