Can you generate a variadic template pack from a size and its content?

c++, c++11, templates, variadic-templates

Solution

With a bit of TMP, this isn't that hard after all:

template<unsigned ToGo, class T, T Arg, template<T...> class Target, T... Args>
struct generate_pack
  : generate_pack<ToGo-1, T, Arg, Target, Args..., Arg>
{ // build up the 'Args' pack by appending 'Arg' ...
};

template<class T, T Arg, template<T...> class Target, T... Args>
struct generate_pack<0, T, Arg, Target, Args...>
{ // until there are no more appends to do
  using type = Target<Args...>;
};

template<unsigned Num, class T, T Arg, template<T...> class Target>
using GeneratePack = typename generate_pack<Num, T, Arg, Target>::type;

template<unsigned int... TSIZE>
struct Base{};

template<unsigned int TORDER, unsigned int TDIM> 
struct Derived
  : GeneratePack<TORDER, unsigned, TDIM, Base>
{
};

Live example.

Problem

Consider the following code : ``` template<unsigned int... TSIZE> struct Base {}; template<unsigned int TORDER, unsigned int TDIM> struct Derived : public Base</* TDIM, TDIM, ... TDIM (TORDER times) */> {}; ``` Do you think that a trick exists to correctly generate the template parameters of Base on the second line of this example ? For example I want `Derived<3, 5>` to inherit from `Base<5, 5, 5>`. How to do that ?

Original source