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//
// Copyright 2019 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_RANDOM_INTERNAL_MOCK_HELPERS_H_
#define ABSL_RANDOM_INTERNAL_MOCK_HELPERS_H_
#include <tuple>
#include <type_traits>
#include "absl/base/internal/fast_type_id.h"
#include "absl/types/optional.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
// MockHelpers works in conjunction with MockOverloadSet, MockingBitGen, and
// BitGenRef to enable the mocking capability for absl distribution functions.
//
// MockingBitGen registers mocks based on the typeid of a mock signature, KeyT,
// which is used to generate a unique id.
//
// KeyT is a signature of the form:
// result_type(discriminator_type, std::tuple<args...>)
// The mocked function signature will be composed from KeyT as:
// result_type(args...)
//
class MockHelpers {
using IdType = ::absl::base_internal::FastTypeIdType;
// Given a key signature type used to index the mock, extract the components.
// KeyT is expected to have the form:
// result_type(discriminator_type, arg_tuple_type)
template <typename KeyT>
struct KeySignature;
template <typename ResultT, typename DiscriminatorT, typename ArgTupleT>
struct KeySignature<ResultT(DiscriminatorT, ArgTupleT)> {
using result_type = ResultT;
using discriminator_type = DiscriminatorT;
using arg_tuple_type = ArgTupleT;
};
// Detector for InvokeMock.
template <class T>
using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock(
std::declval<IdType>(), std::declval<void*>(), std::declval<void*>()));
// Empty implementation of InvokeMock.
template <typename KeyT, typename ReturnT, typename ArgTupleT, typename URBG,
typename... Args>
static absl::optional<ReturnT> InvokeMockImpl(char, URBG*, Args&&...) {
return absl::nullopt;
}
// Non-empty implementation of InvokeMock.
template <typename KeyT, typename ReturnT, typename ArgTupleT, typename URBG,
typename = invoke_mock_t<URBG>, typename... Args>
static absl::optional<ReturnT> InvokeMockImpl(int, URBG* urbg,
Args&&... args) {
ArgTupleT arg_tuple(std::forward<Args>(args)...);
ReturnT result;
if (urbg->InvokeMock(::absl::base_internal::FastTypeId<KeyT>(), &arg_tuple,
&result)) {
return result;
}
return absl::nullopt;
}
public:
// Invoke a mock for the KeyT (may or may not be a signature).
//
// KeyT is used to generate a typeid-based lookup key for the mock.
// KeyT is a signature of the form:
// result_type(discriminator_type, std::tuple<args...>)
// The mocked function signature will be composed from KeyT as:
// result_type(args...)
//
// An instance of arg_tuple_type must be constructable from Args..., since
// the underlying mechanism requires a pointer to an argument tuple.
template <typename KeyT, typename URBG, typename... Args>
static auto MaybeInvokeMock(URBG* urbg, Args&&... args)
-> absl::optional<typename KeySignature<KeyT>::result_type> {
// Use function overloading to dispatch to the implemenation since
// more modern patterns (e.g. require + constexpr) are not supported in all
// compiler configurations.
return InvokeMockImpl<KeyT, typename KeySignature<KeyT>::result_type,
typename KeySignature<KeyT>::arg_tuple_type, URBG>(
0, urbg, std::forward<Args>(args)...);
}
// Acquire a mock for the KeyT (may or may not be a signature).
//
// KeyT is used to generate a typeid-based lookup for the mock.
// KeyT is a signature of the form:
// result_type(discriminator_type, std::tuple<args...>)
// The mocked function signature will be composed from KeyT as:
// result_type(args...)
template <typename KeyT, typename MockURBG>
static auto MockFor(MockURBG& m) -> decltype(
std::declval<MockURBG>()
.template RegisterMock<typename KeySignature<KeyT>::result_type,
typename KeySignature<KeyT>::arg_tuple_type>(
std::declval<IdType>())) {
return m.template RegisterMock<typename KeySignature<KeyT>::result_type,
typename KeySignature<KeyT>::arg_tuple_type>(
::absl::base_internal::FastTypeId<KeyT>());
}
};
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_RANDOM_INTERNAL_MOCK_HELPERS_H_
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