| // Copyright 2015 The Cobalt Authors. All Rights Reserved. |
| // |
| // 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 COBALT_BASE_POLYMORPHIC_EQUATABLE_H_ |
| #define COBALT_BASE_POLYMORPHIC_EQUATABLE_H_ |
| |
| #include "cobalt/base/polymorphic_downcast.h" |
| #include "cobalt/base/type_id.h" |
| |
| namespace base { |
| |
| // Derive from this class from the base class of a class hierarchy in order to |
| // provide your hierarchy with the functionality to test for equivalence between |
| // different instances without knowing what the type of each instance is. |
| // You will also need to add the line |
| // DEFINE_POLYMORPHIC_EQUATABLE_TYPE(MyDerivedClass) |
| // to the public section of each of your derived classes, to have them |
| // automatically implement the virtual methods declared in PolymorphicEquatable. |
| // You will additionally have to ensure that operator==() is defined, as it |
| // will be used to test for equality among objects of the same type. |
| class PolymorphicEquatable { |
| public: |
| virtual bool Equals(const PolymorphicEquatable& other) const = 0; |
| virtual base::TypeId GetTypeId() const = 0; |
| }; |
| |
| // Used to provide type-safe equality checking even when the exact |
| // PolymorphicEquatable type is unknown. For any class T that is intended to be |
| // a descendant of PolymorphicEquatable, it should call this macro in the public |
| // section of its class declaration. |
| #define DEFINE_POLYMORPHIC_EQUATABLE_TYPE(DerivedClassType) \ |
| bool Equals(const PolymorphicEquatable& other) const override { \ |
| return base::GetTypeId<DerivedClassType>() == other.GetTypeId() && \ |
| *this == \ |
| *base::polymorphic_downcast<const DerivedClassType*>(&other); \ |
| } \ |
| \ |
| base::TypeId GetTypeId() const override { \ |
| return base::GetTypeId<DerivedClassType>(); \ |
| } |
| |
| } // namespace base |
| |
| #endif // COBALT_BASE_POLYMORPHIC_EQUATABLE_H_ |