Thread: Vector of `std::unique_ptr' initialization

Hi,

Code:

struct base {
    virtual ~base()=default;
};


template<typename... Types>
class collection {
    std::vector<std::unique_ptr<base>> m_values{std::unique_ptr<base>{new Types}...};
};


struct test: base {
};


int main()
{
    collection<test> c;
}

GCC gives me

Code:

/usr/include/c++/5.1.0/bits/stl_construct.h:75:7: error: use of deleted function ‘std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = base; _Dp = std::default_delete<base>]’
     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }

I know that `std::unique_ptr' is movable only, but I can't figure out why this program is trying to copy construct one?

Ok, I could also have used the code below but changing the context doesn't change the problem (I guess). The program still tries to call the deleted copy constructor:

Code:

struct base {
    virtual ~base()=default;
};


struct test: base {
};


int main()
{
    std::vector<std::unique_ptr<base>> values{std::unique_ptr<base>{new test}};
}

As far as I know,

Code:

std::unique_ptr<base>{new test}

is a rvalue and should therefore be moved into the vector instead of being copied. Obviously I'm using the unique pointer the wrong way, but i still don't understand why... :/

Ok I think I figured it out. The problem is the initializer list of the vector, which can't move objects but only copy them. Therefore using the initializer list won't work for objects of type `std::unique_ptr'.