meta/base.hpp

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/*
 
Copyright 2025 Matthew Tolman
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
   http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 
*/
 
#ifndef MTCORE_META_BASE_HPP
#define MTCORE_META_BASE_HPP


namespace mtcore::meta {
  template<bool Cond, typename L, typename R>
  struct If;
 
  template<typename L, typename R>
  struct If<true, L, R> {
    using T                     = L;
    static constexpr auto value = true;
  };
 
  template<typename L, typename R>
  struct If<false, L, R> {
    using T                     = R;
    static constexpr auto value = false;
  };

  template<bool... Conds>
  struct And {
    static constexpr auto value = (Conds && ...);
  };

  template<bool... Conds>
  struct Or {
    static constexpr auto value = (Conds || ...);
  };

  template<int... T>
  struct IntList;
 
  template<>
  struct IntList<> {
    static constexpr size_t size = 0;
    static constexpr bool empty  = true;
    template<int>
    static constexpr bool has = false;
  };
 
  template<int Head, int... Rest>
  struct IntList<Head, Rest...> {
    static constexpr auto head   = Head;
    using Next                   = IntList<Rest...>;
    static constexpr size_t size = 1 + Next::size;
    static constexpr bool empty  = false;
 
    template<int Needle>
    static constexpr bool has = Needle == Head || Next::template has<Needle>;
  };
 
  static_assert(IntList<1, 2, 3>::has<3>);
  static_assert(IntList<1, 2, 3>::has<2>);
  static_assert(!IntList<1, 2, 3>::has<6>);

  template<typename... T>
  struct TypeList;
 
  template<>
  struct TypeList<> {
    static constexpr size_t size = 0;
    static constexpr bool empty  = 0;
  };
 
  template<typename Head, typename... Rest>
  struct TypeList<Head, Rest...> {
    using T                      = Head;
    using Next                   = TypeList<Rest...>;
    static constexpr size_t size = 1 + Next::size;
    static constexpr bool empty  = false;
  };

  template<typename... T>
  struct ConcatIntList;
 
  template<typename L>
  struct ConcatIntList<L> {
    using T = L;
  };
 
  template<int... L1, int... L2, typename... LRest>
  struct ConcatIntList<IntList<L1...>, IntList<L2...>, LRest...> {
    using T = typename ConcatIntList<IntList<L1..., L2...>, LRest...>::T;
  };
 
  static_assert(ConcatIntList<IntList<1, 2>, IntList<3>>::T::has<3>);
  static_assert(!ConcatIntList<IntList<1, 2>, IntList<3>>::T::has<6>);
}  // namespace mtcore::meta
 
#endif  // MTCORE_META_BASE_HPP