Checking type of parameter pack using enable_if

Question

Since there is a restriction on allowed non-type variadic templates, I am trying to write a function taking an arbitrary number of doubles using enable_if. In essen

Answer 1

Here is a generic approach – a TMP for binary folding, using C++14. First, let's define the basic combining operations:

#include 

struct and_op
{
    using type = bool;
    using identity = std::true_type;
    template  static constexpr bool value = A && B;
};

struct or_op
{
    using type = bool;
    using identity = std::false_type;
    template  static constexpr bool value = A || B;
};

Now the actual fold mechanic:

template 
struct fold;

template 
struct fold : Op::identity {};

template 
struct fold
    : std::integral_constant {};

template 
struct fold
    : std::integral_constant::value>> {};

Next, we need a way to create unary traits from binary traits by binding:

template