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//
// 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_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
#define ABSL_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
#include <utility>
#include <type_traits>
#include "absl/base/config.h"
#include "absl/base/internal/fast_type_id.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
// DistributionCaller provides an opportunity to overload the general
// mechanism for calling a distribution, allowing for mock-RNG classes
// to intercept such calls.
template <typename URBG>
struct DistributionCaller {
static_assert(!std::is_pointer<URBG>::value,
"You must pass a reference, not a pointer.");
// SFINAE to detect whether the URBG type includes a member matching
// bool InvokeMock(base_internal::FastTypeIdType, void*, void*).
//
// These live inside BitGenRef so that they have friend access
// to MockingBitGen. (see similar methods in DistributionCaller).
template <template <class...> class Trait, class AlwaysVoid, class... Args>
struct detector : std::false_type {};
template <template <class...> class Trait, class... Args>
struct detector<Trait, absl::void_t<Trait<Args...>>, Args...>
: std::true_type {};
template <class T>
using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock(
std::declval<::absl::base_internal::FastTypeIdType>(),
std::declval<void*>(), std::declval<void*>()));
using HasInvokeMock = typename detector<invoke_mock_t, void, URBG>::type;
// Default implementation of distribution caller.
template <typename DistrT, typename... Args>
static typename DistrT::result_type Impl(std::false_type, URBG* urbg,
Args&&... args) {
DistrT dist(std::forward<Args>(args)...);
return dist(*urbg);
}
// Mock implementation of distribution caller.
// The underlying KeyT must match the KeyT constructed by MockOverloadSet.
template <typename DistrT, typename... Args>
static typename DistrT::result_type Impl(std::true_type, URBG* urbg,
Args&&... args) {
using ResultT = typename DistrT::result_type;
using ArgTupleT = std::tuple<absl::decay_t<Args>...>;
using KeyT = ResultT(DistrT, ArgTupleT);
ArgTupleT arg_tuple(std::forward<Args>(args)...);
ResultT result;
if (!urbg->InvokeMock(::absl::base_internal::FastTypeId<KeyT>(), &arg_tuple,
&result)) {
auto dist = absl::make_from_tuple<DistrT>(arg_tuple);
result = dist(*urbg);
}
return result;
}
// Default implementation of distribution caller.
template <typename DistrT, typename... Args>
static typename DistrT::result_type Call(URBG* urbg, Args&&... args) {
return Impl<DistrT, Args...>(HasInvokeMock{}, urbg,
std::forward<Args>(args)...);
}
};
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTION_CALLER_H_
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