Ioss_Enumerate.h

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// https://www.reedbeta.com/blog/python-like-enumerate-in-cpp17/
// std::vector<Thing> things;
// ...
// for (auto [i, thing] : enumerate(things))
// {
//     .. `i` gets the index and `thing` gets the Thing in each iteration
// }
 
#include <tuple>
 
namespace Ioss {
  template <typename T, typename TIter = decltype(std::begin(std::declval<T>())),
            typename = decltype(std::end(std::declval<T>()))>
  constexpr auto enumerate(T &&iterable)
  {
    struct iterator
    {
      size_t i;
      TIter  iter;
      bool   operator!=(const iterator &other) const { return iter != other.iter; }
      void   operator++()
      {
        ++i;
        ++iter;
      }
      auto operator*() const { return std::tie(i, *iter); }
    };
    struct iterable_wrapper
    {
      T    iterable;
      auto begin() { return iterator{0, std::begin(iterable)}; }
      auto end() { return iterator{0, std::end(iterable)}; }
    };
    return iterable_wrapper{std::forward<T>(iterable)};
  }
} // namespace Ioss