Question

I have a class with one std::unique_ptr as class member. I was wondering, how to correctly define the copy constructor, since I’m getting the following compiler error message: error C2248: std::unique_ptr<_Ty>::unique_ptr : cannot access private member declared in class 'std::unique_ptr<_Ty>. My class design looks something like:

template <typename T>
class Foo{
    public:
        Foo(){};
        Foo( Bar<T> *, int );
        Foo( const Foo<T> & );
        ~Foo(){};

        void swap( Foo<T> & );
        Foo<T> operator = ( Foo<T> );

    private:
        std::unique_ptr<Bar> m_ptrBar;
        int m_Param1;

};

template < typename T >
Foo<T>::Foo( const Foo<T> & refFoo )
:m_ptrBar(refFoo.m_ptrBar), 
m_Param1(refFoo.m_Param1)
{
    // error here!
}

template < typename T >
void Foo<T>::swap( Foo<T> & refFoo ){
    using std::swap;
    swap(m_ptrBar, refFoo.m_ptrBar);
    swap(m_Param1, refFoo.m_Param1);
 }

 template < typename T >
 Foo<T> Foo<T>::operator = ( Foo<T> Elem ){
    Elem.swap(*this);
    return (*this);
 }

Answer 1

Assuming the goal is to copy-construct the uniquely-owned Bar,

template < typename T >
Foo<T>::Foo( const Foo<T> & refFoo )
: m_ptrBar(refFoo.m_ptrBar ? new Bar(*refFoo.m_ptrBar) : nullptr),
  m_Param1(refFoo.m_Param1)
{
}