arrow/util/compare.h

0001 // Licensed to the Apache Software Foundation (ASF) under one
0002 // or more contributor license agreements.  See the NOTICE file
0003 // distributed with this work for additional information
0004 // regarding copyright ownership.  The ASF licenses this file
0005 // to you under the Apache License, Version 2.0 (the
0006 // "License"); you may not use this file except in compliance
0007 // with the License.  You may obtain a copy of the License at
0008 //
0009 //   http://www.apache.org/licenses/LICENSE-2.0
0010 //
0011 // Unless required by applicable law or agreed to in writing,
0012 // software distributed under the License is distributed on an
0013 // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
0014 // KIND, either express or implied.  See the License for the
0015 // specific language governing permissions and limitations
0016 // under the License.
0017
0018 #pragma once
0019
0020 #include <memory>
0021 #include <type_traits>
0022 #include <utility>
0023
0024 #include "arrow/util/macros.h"
0025
0026 namespace arrow {
0027 namespace util {
0028
0029 /// CRTP helper for declaring equality comparison. Defines operator== and operator!=
0030 template <typename T>
0031 class EqualityComparable {
0032  public:
0033   ~EqualityComparable() {
0034     static_assert(
0035         std::is_same<decltype(std::declval<const T>().Equals(std::declval<const T>())),
0036                      bool>::value,
0037         "EqualityComparable depends on the method T::Equals(const T&) const");
0038   }
0039
0040   template <typename... Extra>
0041   bool Equals(const std::shared_ptr<T>& other, Extra&&... extra) const {
0042     if (other == NULLPTR) {
0043       return false;
0044     }
0045     return cast().Equals(*other, std::forward<Extra>(extra)...);
0046   }
0047
0048   struct PtrsEqual {
0049     bool operator()(const std::shared_ptr<T>& l, const std::shared_ptr<T>& r) const {
0050       return l->Equals(*r);
0051     }
0052   };
0053
0054   friend bool operator==(T const& a, T const& b) { return a.Equals(b); }
0055   friend bool operator!=(T const& a, T const& b) { return !(a == b); }
0056
0057  private:
0058   const T& cast() const { return static_cast<const T&>(*this); }
0059 };
0060
0061 }  // namespace util
0062 }  // namespace arrow