chromium/third_party/abseil-cpp/absl/hash/internal/spy_hash_state.h

// Copyright 2018 The Abseil 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
//
//      https://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 ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_
#define ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_

#include <algorithm>
#include <ostream>
#include <string>
#include <vector>

#include "absl/hash/hash.h"
#include "absl/strings/match.h"
#include "absl/strings/str_format.h"
#include "absl/strings/str_join.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace hash_internal {

// SpyHashState is an implementation of the HashState API that simply
// accumulates all input bytes in an internal buffer. This makes it useful
// for testing AbslHashValue overloads (so long as they are templated on the
// HashState parameter), since it can report the exact hash representation
// that the AbslHashValue overload produces.
//
// Sample usage:
// EXPECT_EQ(SpyHashState::combine(SpyHashState(), foo),
//           SpyHashState::combine(SpyHashState(), bar));
template <typename T>
class SpyHashStateImpl : public HashStateBase<SpyHashStateImpl<T>> { … };

template <typename T>
bool SpyHashStateImpl<T>::direct_absl_hash_value_error_;

template <bool& B>
struct OdrUse { … };

template <void (*)()>
struct RunOnStartup { … };

template <void (*f)()>
bool RunOnStartup<f>::run = …;

template <
    typename T, typename U,
    // Only trigger for when (T != U),
    typename = absl::enable_if_t<!std::is_same<T, U>::value>,
    // This statement works in two ways:
    //  - First, it instantiates RunOnStartup and forces the initialization of
    //    `run`, which set the global variable.
    //  - Second, it triggers a SFINAE error disabling the overload to prevent
    //    compile time errors. If we didn't disable the overload we would get
    //    ambiguous overload errors, which we don't want.
    int = RunOnStartup<SpyHashStateImpl<T>::SetDirectAbslHashValueError>::run>
void AbslHashValue(SpyHashStateImpl<T>, const U&);

SpyHashState;

}  // namespace hash_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_