draconisplusplus/include/rfl/internal/Getter.hpp

#ifndef RFL_INTERNAL_GETTER_HPP_
#define RFL_INTERNAL_GETTER_HPP_

#include <tuple>
#include <variant>

#include "StringLiteral.hpp"
#include "find_index.hpp"

namespace rfl::internal {

  // ----------------------------------------------------------------------------

  template <class NamedTupleType>
  struct Getter;

  // ----------------------------------------------------------------------------

  /// Default case - anything that cannot be explicitly matched.
  template <class NamedTupleType>
  struct Getter {
   public:
    /// Retrieves the indicated value from the tuple.
    template <int _index>
    static inline auto& get(NamedTupleType& _tup) {
      return std::get<_index>(_tup.values());
    }

    /// Gets a field by name.
    template <StringLiteral _field_name>
    static inline auto& get(NamedTupleType& _tup) {
      constexpr auto index = find_index<_field_name, typename NamedTupleType::Fields>();
      return Getter<NamedTupleType>::template get<index>(_tup);
    }

    /// Gets a field by the field type.
    template <class Field>
    static inline auto& get(NamedTupleType& _tup) {
      constexpr auto index = find_index<Field::name_, typename NamedTupleType::Fields>();
      static_assert(
        std::is_same<
          typename std::tuple_element<index, typename NamedTupleType::Fields>::type::Type,
          typename Field::Type>(),
        "If two fields have the same name, "
        "their type must be the same as "
        "well."
      );
      return Getter<NamedTupleType>::template get<index>(_tup);
    }

    /// Retrieves the indicated value from the tuple.
    template <int _index>
    static inline const auto& get_const(const NamedTupleType& _tup) {
      return std::get<_index>(_tup.values());
    }

    /// Gets a field by name.
    template <StringLiteral _field_name>
    static inline const auto& get_const(const NamedTupleType& _tup) {
      constexpr auto index = find_index<_field_name, typename NamedTupleType::Fields>();
      return Getter<NamedTupleType>::template get_const<index>(_tup);
    }

    /// Gets a field by the field type.
    template <class Field>
    static inline const auto& get_const(const NamedTupleType& _tup) {
      constexpr auto index = find_index<Field::name_, typename NamedTupleType::Fields>();
      static_assert(
        std::is_same<
          typename std::tuple_element<index, typename NamedTupleType::Fields>::type::Type,
          typename Field::Type>(),
        "If two fields have the same name, "
        "their type must be the same as "
        "well."
      );
      return Getter<NamedTupleType>::template get_const<index>(_tup);
    }
  };

  // ----------------------------------------------------------------------------

  /// For handling std::variant.
  template <class... NamedTupleTypes>
  struct Getter<std::variant<NamedTupleTypes...>> {
   public:
    /// Retrieves the indicated value from the tuple.
    template <int _index>
    static inline auto& get(std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](auto& _t) -> auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_t)>;
        return Getter<NamedTupleType>::template get<_index>(_t);
      };
      return std::visit(apply, _tup);
    }

    /// Gets a field by name.
    template <StringLiteral _field_name>
    static inline auto& get(std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](auto& _t) -> auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_t)>;
        return Getter<NamedTupleType>::template get<_field_name>(_t);
      };
      return std::visit(apply, _tup);
    }

    /// Gets a field by the field type.
    template <class Field>
    static inline auto& get(std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](auto& _t) -> auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_t)>;
        return Getter<NamedTupleType>::template get<Field>(_t);
      };
      return std::visit(apply, _tup);
    }

    /// Retrieves the indicated value from the tuple.
    template <int _index>
    static inline const auto& get_const(const std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](const auto& _tup) -> const auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_tup)>;
        return Getter<NamedTupleType>::template get_const<_index>(_tup);
      };
      return std::visit(apply, _tup);
    }

    /// Gets a field by name.
    template <StringLiteral _field_name>
    static inline const auto& get_const(const std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](const auto& _t) -> const auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_t)>;
        return Getter<NamedTupleType>::template get_const<_field_name>(_t);
      };
      return std::visit(apply, _tup);
    }

    /// Gets a field by the field type.
    template <class Field>
    static inline const auto& get_const(const std::variant<NamedTupleTypes...>& _tup) {
      const auto apply = [](const auto& _t) -> const auto& {
        using NamedTupleType = std::remove_cvref_t<decltype(_t)>;
        return Getter<NamedTupleType>::template get_const<Field>(_t);
      };
      return std::visit(apply, _tup);
    }
  };

  // ----------------------------------------------------------------------------

} // namespace rfl::internal

#endif