src/dawn/native/ObjectContentHasher.h

// Copyright 2020 The Dawn Authors
//
// 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 SRC_DAWN_NATIVE_OBJECTCONTENTHASHER_H_
#define SRC_DAWN_NATIVE_OBJECTCONTENTHASHER_H_

#include <map>
#include <string>
#include <utility>
#include <vector>

#include "dawn/common/HashUtils.h"

namespace dawn::native {

// ObjectContentHasher records a hash that can be used as a key to lookup a cached object in a
// cache.
class ObjectContentHasher {
  public:
    // Record calls the appropriate record function based on the type.
    template <typename T, typename... Args>
    void Record(const T& value, const Args&... args) {
        RecordImpl<T, Args...>::Call(this, value, args...);
    }

    size_t GetContentHash() const;

  private:
    template <typename T, typename... Args>
    struct RecordImpl {
        static constexpr void Call(ObjectContentHasher* recorder,
                                   const T& value,
                                   const Args&... args) {
            HashCombine(&recorder->mContentHash, value, args...);
        }
    };

    template <typename T>
    struct RecordImpl<T*> {
        static constexpr void Call(ObjectContentHasher* recorder, T* obj) {
            // Calling Record(objPtr) is not allowed. This check exists to only prevent such
            // mistakes.
            static_assert(obj == nullptr);
        }
    };

    template <typename T>
    struct RecordImpl<std::vector<T>> {
        static constexpr void Call(ObjectContentHasher* recorder, const std::vector<T>& vec) {
            recorder->RecordIterable<std::vector<T>>(vec);
        }
    };

    template <typename T, typename E>
    struct RecordImpl<std::map<T, E>> {
        static constexpr void Call(ObjectContentHasher* recorder, const std::map<T, E>& map) {
            recorder->RecordIterable<std::map<T, E>>(map);
        }
    };

    template <typename IteratorT>
    constexpr void RecordIterable(const IteratorT& iterable) {
        for (auto it = iterable.begin(); it != iterable.end(); ++it) {
            Record(*it);
        }
    }

    template <typename T, typename E>
    struct RecordImpl<std::pair<T, E>> {
        static constexpr void Call(ObjectContentHasher* recorder, const std::pair<T, E>& pair) {
            recorder->Record(pair.first);
            recorder->Record(pair.second);
        }
    };

    size_t mContentHash = 0;
};

template <>
struct ObjectContentHasher::RecordImpl<std::string> {
    static constexpr void Call(ObjectContentHasher* recorder, const std::string& str) {
        recorder->RecordIterable<std::string>(str);
    }
};

}  // namespace dawn::native

#endif  // SRC_DAWN_NATIVE_OBJECTCONTENTHASHER_H_