模板特化功能参数计数

Question

Ok, an update to my previous question about templates ( I'm such a noob on this field )... I resumed most of my questions to: Is it possible to have a different parameter count for a member function, depending on the template parameter used on the class declaration?

For example, a constructor:

template <typename Type, unsigned ElementCount>
class TVector
    {
    public:
    Type Values[ElementCount];

    TVector ( ElementCount number of Type here )
        { ...

Is this possible? Or perhaps a setter:

SetValues ( ElementCount number of Type here );

EDIT: Ok, my mistake, i did not explain fully. This vector is a trigonometry vector, not an array of elements. So, it should support 2, 3 or 4 values.

As for the constructor, i wanted to be able to do something like: TVector xpto ( 0.0f, 0.0f, 0.0f, 1.0f );

As for compiler, i'm using gcc, and dunno if it's safe to enable more recent c++ standards. It does complain about it, when i enable them. So, no enable_if for me :)

Thanks.

Answer 1

The member function can have as parameter a std::initializer_list<T> type that will let it access any number of objects of type const T. In that case, ElemCount, in the class template, can be removed as you don't have to specify number of arguments.

template <typename Type>
class TVector
    {
    public:    

    TVector ( std::initializer_list<Type> l )
        { ...

Answer 2

Yes, you can, using std::enable_if .

template <typename T, typename ... Ts>
struct AllSameAsT : public std::false_type
{
};

template <typename T>
struct AllSameAsT<T> : public std::true_type
{
};

template <typename T, typename T, typename ... Ts>
struct AllSameAsT : public AllSameAsT<T, Ts...>
{
};


template <typename Type, unsigned ElementCount>
class TVector
    {
    public:
    template <typename ... Ts, typename = std::enable_if_t<AllSameAsT<Type, Ts...>::value && (sizeof...(Ts) == ElementCount)>
    TVector (Ts... ts);
    };

If you don't have C++14, you would also need to add

template< bool B, class T = void >
using enable_if_t = typename enable_if<B,T>::type;

As JosephMansfield has pointed out in the comments, a simpler solution might be to just accept an std::array<Type, ElementCount> .