92 lines
3.4 KiB
C++
92 lines
3.4 KiB
C++
//
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef ABSL_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
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#define ABSL_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
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#include <utility>
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#include "absl/base/config.h"
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#include "absl/base/internal/fast_type_id.h"
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#include "absl/utility/utility.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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// DistributionCaller provides an opportunity to overload the general
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// mechanism for calling a distribution, allowing for mock-RNG classes
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// to intercept such calls.
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template <typename URBG>
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struct DistributionCaller {
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// SFINAE to detect whether the URBG type includes a member matching
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// bool InvokeMock(base_internal::FastTypeIdType, void*, void*).
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//
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// These live inside BitGenRef so that they have friend access
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// to MockingBitGen. (see similar methods in DistributionCaller).
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template <template <class...> class Trait, class AlwaysVoid, class... Args>
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struct detector : std::false_type {};
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template <template <class...> class Trait, class... Args>
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struct detector<Trait, absl::void_t<Trait<Args...>>, Args...>
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: std::true_type {};
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template <class T>
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using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock(
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std::declval<::absl::base_internal::FastTypeIdType>(),
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std::declval<void*>(), std::declval<void*>()));
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using HasInvokeMock = typename detector<invoke_mock_t, void, URBG>::type;
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// Default implementation of distribution caller.
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template <typename DistrT, typename... Args>
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static typename DistrT::result_type Impl(std::false_type, URBG* urbg,
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Args&&... args) {
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DistrT dist(std::forward<Args>(args)...);
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return dist(*urbg);
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}
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// Mock implementation of distribution caller.
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// The underlying KeyT must match the KeyT constructed by MockOverloadSet.
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template <typename DistrT, typename... Args>
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static typename DistrT::result_type Impl(std::true_type, URBG* urbg,
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Args&&... args) {
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using ResultT = typename DistrT::result_type;
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using ArgTupleT = std::tuple<absl::decay_t<Args>...>;
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using KeyT = ResultT(DistrT, ArgTupleT);
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ArgTupleT arg_tuple(std::forward<Args>(args)...);
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ResultT result;
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if (!urbg->InvokeMock(::absl::base_internal::FastTypeId<KeyT>(), &arg_tuple,
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&result)) {
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auto dist = absl::make_from_tuple<DistrT>(arg_tuple);
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result = dist(*urbg);
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}
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return result;
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}
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// Default implementation of distribution caller.
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template <typename DistrT, typename... Args>
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static typename DistrT::result_type Call(URBG* urbg, Args&&... args) {
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return Impl<DistrT, Args...>(HasInvokeMock{}, urbg,
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std::forward<Args>(args)...);
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}
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};
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
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