draconisplusplus/include/rfl/internal/remove_fields.hpp

#ifndef RFL_INTERNAL_REMOVEFIELDS_HPP_
#define RFL_INTERNAL_REMOVEFIELDS_HPP_

#include <algorithm>
#include <tuple>
#include <type_traits>

#include "../NamedTuple.hpp"
#include "../define_named_tuple.hpp"
#include "StringLiteral.hpp"

namespace rfl {
  namespace internal {

    /// Recursively builds a new NamedTuple type from the FieldTypes, leaving
    /// out the field signified by _name.
    template <
        class _OldNamedTupleType,
        StringLiteral _name,
        class _NewNamedTupleType,
        int _i>
    struct remove_single_field;

    /// Special case - _i == 0
    template <
        class _OldNamedTupleType,
        StringLiteral _name,
        class _NewNamedTupleType>
    struct remove_single_field<
        _OldNamedTupleType,
        _name,
        _NewNamedTupleType,
        0> {
      using type = _NewNamedTupleType;
    };

    /// General case.
    template <
        class _OldNamedTupleType,
        StringLiteral _name,
        class _NewNamedTupleType,
        int _i>
    struct remove_single_field {
      using OldNamedTupleType = std::remove_cvref_t<_OldNamedTupleType>;

      constexpr static int num_fields =
          std::tuple_size_v<typename OldNamedTupleType::Fields>;

      using FieldType = std::remove_cvref_t<typename std::tuple_element<
          num_fields - _i,
          typename OldNamedTupleType::Fields>::type>;

      using NewNamedTupleType = std::conditional_t<
          _name == FieldType::name_,
          _NewNamedTupleType,
          define_named_tuple_t<_NewNamedTupleType, FieldType>>;

      using type = typename remove_single_field<
          OldNamedTupleType,
          _name,
          NewNamedTupleType,
          _i - 1>::type;
    };

    /// Recursively removes all of the fields signified by _head and _tail from
    /// the NamedTupleType.
    template <
        class _NamedTupleType,
        StringLiteral _head,
        StringLiteral... _tail>
    struct remove_fields;

    /// Special case - only head is left.
    template <class _NamedTupleType, StringLiteral _head>
    struct remove_fields<_NamedTupleType, _head> {
      using NamedTupleType = std::remove_cvref_t<_NamedTupleType>;

      constexpr static int num_fields =
          std::tuple_size_v<typename NamedTupleType::Fields>;

      using type = typename remove_single_field<
          NamedTupleType,
          _head,
          NamedTuple<>,
          num_fields>::type;
    };

    /// General case.
    template <
        class _NamedTupleType,
        StringLiteral _head,
        StringLiteral... _tail>
    struct remove_fields {
      using NamedTupleType = std::remove_cvref_t<_NamedTupleType>;

      constexpr static int num_fields =
          std::tuple_size_v<typename NamedTupleType::Fields>;

      using NewNamedTupleType = typename remove_single_field<
          NamedTupleType,
          _head,
          NamedTuple<>,
          num_fields>::type;

      using type = typename remove_fields<NewNamedTupleType, _tail...>::type;
    };

  } // namespace internal
} // namespace rfl

#endif // RFL_REMOVEFIELDS_HPP_