A variadic template method to accept a given number of doubles?

Question

template  class myclass
{
public:
    template  void mymethod(Args... args)
    {
       // Do interesting stuff
    } 
};
         


        

Answer 1

For the number of arguments constraint you can easily check if sizeof...(Args) == N but for checking if all the arguments are doubles you need to build a recursive type trait that checks std::is_same for each of the arguments.

template
struct are_same : std::true_type 
{};

template
struct are_same : std::true_type
{};

template
struct are_same :
    std::integral_constant::value && are_same::value)>
{};

Notice are_same is first declared and then specialized.

Then just implement the constraint in your method return type using std::enable_if by taking advantage of SFINAE.

template  class myclass
{
public:
    template 
    typename std::enable_if<(are_same::value && sizeof...(Args) == N), void>::type
    /* void */ mymethod(Args... args)
    {
        // Do interesting stuff
    } 
};