Question

I get Compiler Error C2248 when i try to compile the following code:

#include <list>
#include <memory>
using namespace std;


class data
{
public:

    static data parse()
    {
        data d;
        data::parse(d);
        return d;
    }

    list<std::unique_ptr<data>> l;

private:

    static void parse(data& node)
    {       }
};


int main()
{

    return 0;
}

Why? How can i fix this?

Note: I have no problem using std::shared_ptr instead of std::unique_ptr.

Answer 1

You need to provide move operations for your type:

data(data&& other)
    : l(std::move(other.l))
{
}

data& operator=(data&& other)
{
    l = std::move(other.l);
    return *this;
}

And, since you’ll have added a user-declared constructor, you’ll also need a user-declared default constructor:

data() { }

My understanding is that your code is correct as-is, per the final C++11 language standard. Visual C++ does not fully implement the final specification for when move operations are implicitly generated (as of the Visual C++ 2012 RC). The specification for when implicit move operations are generated changed several times very late in the standardization process.

If you have a class type C that has any data member that is movable but noncopyable, Visual C++ will not generate an implicit move constructor or move assignment operator, and the implicit copy constructor and copy assignment operator are both suppressed by the presence of the move-only data member. In other words, if you want ot aggregate move-only types, you must provide the move operations for the aggregating class yourself.

(At least, this is my understanding from experimentation with the compiler.)