#include <memory>    // for std::unique_ptr
#include <utility>   // for std::move
#include <vector>    // for std::vector

struct bar {};

struct foo
{
    using vtype = std::vector<std::unique_ptr<bar>>;
    foo(vtype v) : _v(std::move(v)) { }
private:
    vtype _v;
};

int main()
{
    foo::vtype v;
    foo x(std::move(v));
}