Sorting a vector of unique_ptr in VS 2013

Question

I am attempting to make a Deck class that holds a vector of unique_ptr<Card>, but attempting to sort the vector results in this error:

Error 1 error C2280: 'std::unique_ptr>:: unique_ptr(const std::unique_ptr<_Ty,std::default_delete<_Ty>> &)' : attempting to reference a deleted function

Looking through Stack Overflow, it looks like there is a bug in VS 2013 where vectors incorrectly tries to copy unique_ptrs instead of moving them, so I attempted to add my own move function to my Deck class, but I still get the error.

Here is a minimal example of the code in question (Card is just a dummy class, with no objects in it):

Deck.h:

#include "Card.h"
#include <vector>
#include <memory>

class Deck
{
public:
typedef std::unique_ptr<Card> cardPtr;

Deck();

Deck(Deck && other)
    : mDeck(std::move(other.mDeck))
{
}

Deck& operator=(Deck other)
{
    swap(*this, other);
    return *this;
}

friend void swap(Deck& lhs, Deck& rhs);

void                                sortDeck();

private:
static bool                         compareCards(cardPtr A, cardPtr B);

private:
std::vector<cardPtr>                mDeck;
};

Deck.cpp:

#include "Deck.h"
#include <algorithm>


Deck::Deck()
{
}

void swap(Deck& lhs, Deck& rhs)
{
using std::swap;
swap(lhs.mDeck, rhs.mDeck);
}


bool Deck::compareCards(cardPtr A, cardPtr B)
{
return true; //dummy- normally would have logic here
}

void Deck::sortDeck()
{
std::sort(mDeck.begin(), mDeck.end(), compareCards); //bug happens here
}

Any ideas about how to fix this? I'm sure I must be missing something fairly obvious, but I have been beating my head against this and googling it for a fair amount of time now, and could use some help.

Answer 1

Your compareCards function takes the unique_ptrs by value, this won't work as they are not copyable (the unique_ptr copy constructor is implicitly deleted due to the presence of move constructors, a copyable unique_ptr wouldn't be very unique would it?).

Change it to

bool compareCards(cardPtr const& A, cardPtr const& B);