text: /*
   * Copyright 2018-present Facebook, Inc.
   *
   * 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.
   */
  
  #pragma once
  
  namespace folly {
  
  enum class ordering : int { lt = -1, eq = 0, gt = 1 };
  
  template <typename T>
  constexpr ordering to_ordering(T c) {
    return c < T(0) ? ordering::lt : c > T(0) ? ordering::gt : ordering::eq;
  }
  
  namespace detail {
  
  template <typename C, ordering o, bool ne>
  struct cmp_pred : private C {
    using C::C;
  
    template <typename A, typename B>
    constexpr bool operator()(A&& a, B&& b) const {
      return ne ^ (C::operator()(static_cast<A&&>(a), static_cast<B&&>(b)) == o);
    }
  };
  
  } // namespace detail
  
  template <typename C>
  struct compare_equal_to : detail::cmp_pred<C, ordering::eq, 0> {
    using detail::cmp_pred<C, ordering::eq, 0>::cmp_pred;
  };
  
  template <typename C>
  struct compare_not_equal_to : detail::cmp_pred<C, ordering::eq, 1> {
    using detail::cmp_pred<C, ordering::eq, 1>::cmp_pred;
  };
  
  template <typename C>
  struct compare_less : detail::cmp_pred<C, ordering::lt, 0> {
    using detail::cmp_pred<C, ordering::lt, 0>::cmp_pred;
  };
  
  template <typename C>
  struct compare_less_equal : detail::cmp_pred<C, ordering::gt, 1> {
    using detail::cmp_pred<C, ordering::gt, 1>::cmp_pred;
  };
  
  template <typename C>
  struct compare_greater : detail::cmp_pred<C, ordering::gt, 0> {
    using detail::cmp_pred<C, ordering::gt, 0>::cmp_pred;
  };
  
  template <typename C>
  struct compare_greater_equal : detail::cmp_pred<C, ordering::lt, 1> {
    using detail::cmp_pred<C, ordering::lt, 1>::cmp_pred;
  };
  
  } // namespace folly
  