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

The bool_pack trick again.

template struct bool_pack;
template 
using all_true = std::is_same, bool_pack>;

Then

template
using are_all_convertible = all_true::value...>;

and finally

template::value>::type>
foo(T... t){ /* code here */}