Question

I’m having an issue with a seemingly complicated problem.

I’m trying to make an iterator class for a zip function (trying to mimic python’s generator zip function).

I have the entire class at http://ideone.com/c7rm40

  template<size_t I = 0, typename... Tp>
  inline typename std::enable_if<(I == sizeof...(Tp)), typename std::tuple<decltype(*Tp)...>>::type
  constructImpl(std::tuple<Tp...> const& its) {

core/StarAlgorithm.hpp|550 col 3| error: expected ‘(’ before ‘constructImpl’
core/StarAlgorithm.hpp|550 col 3| error: expected ‘>’ before ‘constructImpl’
core/StarAlgorithm.hpp|550 col 45| error: template argument 2 is invalid
core/StarAlgorithm.hpp|550 col 47| error: expected ‘::’ before ‘{’ token
core/StarAlgorithm.hpp|550 col 47| error: expected identifier before ‘{’ token
core/StarAlgorithm.hpp|550 col 47| error: expected unqualified-id before ‘{’ token

My question is, is this approach even valid? I can’t figure out why it’s necessarily wrong, or what the compiler wants from me.

But beyond that, if there is a simpler approach I am missing, I would be overjoyed to hear it.

Answer 1

I’m guessing the problem is that *Tp is not a valid expression for decltype.

Maybe try declval?

std::tuple<decltype(*std::declval<Tp>())...>

Or iterator traits:

 std::tuple<typename std::iterator_traits<Tp>::value_type...>