Helper templates for accessing and manipulating template parameter packs

parameter_pack_helpers.hpp

• template <typename T, typename... Args> constexpr size_t index_for_type_v defines the index (position) of type T in the Args... pack. Results in compilation error if the type is not found.

• template <size_t index, typename... Args> using type_by_index defines the type at index in Args....

• template <size_t index, typename... Args> constexpr auto value_by_index(Args&&... args) noexcept returns the value at position index from args.

• template <typename Functor, class... Args> void apply(Functor&& f, Args&&... args) iterates the pack args and calls functor f with each value in the pack.
  Example: apply([](auto&& value){std::cout << value << std::endl;}, 0, -1.0f, "text");

• template <typename... Args, typename Functor> void for_type(Functor&& f) calls functor f for each type in the argument pack. The type is passed using type_wrapper helper template defined in utils/template_magic.hpp.
  Example: for_type<int, float, std::string> ([](auto&& t){ using Type = typename decltype(t)::type; });