// Copyright 2020 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_STATUS_INTERNAL_STATUSOR_INTERNAL_H_
#define ABSL_STATUS_INTERNAL_STATUSOR_INTERNAL_H_
#include <type_traits>
#include <utility>
#include "absl/base/attributes.h"
#include "absl/meta/type_traits.h"
#include "absl/status/status.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
template <typename T>
class ABSL_MUST_USE_RESULT StatusOr;
namespace internal_statusor {
// Detects whether `U` has conversion operator to `StatusOr<T>`, i.e. `operator
// StatusOr<T>()`.
template <typename T, typename U, typename = void>
struct HasConversionOperatorToStatusOr : std::false_type {};
template <typename T, typename U>
void test(char (*)[sizeof(std::declval<U>().operator absl::StatusOr<T>())]);
template <typename T, typename U>
struct HasConversionOperatorToStatusOr<T, U, decltype(test<T, U>(0))>
: std::true_type {};
// Detects whether `T` is constructible or convertible from `StatusOr<U>`.
template <typename T, typename U>
using IsConstructibleOrConvertibleFromStatusOr =
absl::disjunction<std::is_constructible<T, StatusOr<U>&>,
std::is_constructible<T, const StatusOr<U>&>,
std::is_constructible<T, StatusOr<U>&&>,
std::is_constructible<T, const StatusOr<U>&&>,
std::is_convertible<StatusOr<U>&, T>,
std::is_convertible<const StatusOr<U>&, T>,
std::is_convertible<StatusOr<U>&&, T>,
std::is_convertible<const StatusOr<U>&&, T>>;
// Detects whether `T` is constructible or convertible or assignable from
// `StatusOr<U>`.
template <typename T, typename U>
using IsConstructibleOrConvertibleOrAssignableFromStatusOr =
absl::disjunction<IsConstructibleOrConvertibleFromStatusOr<T, U>,
std::is_assignable<T&, StatusOr<U>&>,
std::is_assignable<T&, const StatusOr<U>&>,
std::is_assignable<T&, StatusOr<U>&&>,
std::is_assignable<T&, const StatusOr<U>&&>>;
// Detects whether direct initializing `StatusOr<T>` from `U` is ambiguous, i.e.
// when `U` is `StatusOr<V>` and `T` is constructible or convertible from `V`.
template <typename T, typename U>
struct IsDirectInitializationAmbiguous
: public absl::conditional_t<
std::is_same<absl::remove_cv_t<absl::remove_reference_t<U>>,
U>::value,
std::false_type,
IsDirectInitializationAmbiguous<
T, absl::remove_cv_t<absl::remove_reference_t<U>>>> {};
template <typename T, typename V>
struct IsDirectInitializationAmbiguous<T, absl::StatusOr<V>>
: public IsConstructibleOrConvertibleFromStatusOr<T, V> {};
// Checks against the constraints of the direction initialization, i.e. when
// `StatusOr<T>::StatusOr(U&&)` should participate in overload resolution.
template <typename T, typename U>
using IsDirectInitializationValid = absl::disjunction<
// Short circuits if T is basically U.
std::is_same<T, absl::remove_cv_t<absl::remove_reference_t<U>>>,
absl::negation<absl::disjunction<
std::is_same<absl::StatusOr<T>,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
std::is_same<absl::Status,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
std::is_same<absl::in_place_t,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
IsDirectInitializationAmbiguous<T, U>>>>;
// This trait detects whether `StatusOr<T>::operator=(U&&)` is ambiguous, which
// is equivalent to whether all the following conditions are met:
// 1. `U` is `StatusOr<V>`.
// 2. `T` is constructible and assignable from `V`.
// 3. `T` is constructible and assignable from `U` (i.e. `StatusOr<V>`).
// For example, the following code is considered ambiguous:
// (`T` is `bool`, `U` is `StatusOr<bool>`, `V` is `bool`)
// StatusOr<bool> s1 = true; // s1.ok() && s1.ValueOrDie() == true
// StatusOr<bool> s2 = false; // s2.ok() && s2.ValueOrDie() == false
// s1 = s2; // ambiguous, `s1 = s2.ValueOrDie()` or `s1 = bool(s2)`?
template <typename T, typename U>
struct IsForwardingAssignmentAmbiguous
: public absl::conditional_t<
std::is_same<absl::remove_cv_t<absl::remove_reference_t<U>>,
U>::value,
std::false_type,
IsForwardingAssignmentAmbiguous<
T, absl::remove_cv_t<absl::remove_reference_t<U>>>> {};
template <typename T, typename U>
struct IsForwardingAssignmentAmbiguous<T, absl::StatusOr<U>>
: public IsConstructibleOrConvertibleOrAssignableFromStatusOr<T, U> {};
// Checks against the constraints of the forwarding assignment, i.e. whether
// `StatusOr<T>::operator(U&&)` should participate in overload resolution.
template <typename T, typename U>
using IsForwardingAssignmentValid = absl::disjunction<
// Short circuits if T is basically U.
std::is_same<T, absl::remove_cv_t<absl::remove_reference_t<U>>>,
absl::negation<absl::disjunction<
std::is_same<absl::StatusOr<T>,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
std::is_same<absl::Status,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
std::is_same<absl::in_place_t,
absl::remove_cv_t<absl::remove_reference_t<U>>>,
IsForwardingAssignmentAmbiguous<T, U>>>>;
class Helper {
public:
// Move type-agnostic error handling to the .cc.
static void HandleInvalidStatusCtorArg(Status*);
ABSL_ATTRIBUTE_NORETURN static void Crash(const absl::Status& status);
};
// Construct an instance of T in `p` through placement new, passing Args... to
// the constructor.
// This abstraction is here mostly for the gcc performance fix.
template <typename T, typename... Args>
ABSL_ATTRIBUTE_NONNULL(1) void PlacementNew(void* p, Args&&... args) {
new (p) T(std::forward<Args>(args)...);
}
// Helper base class to hold the data and all operations.
// We move all this to a base class to allow mixing with the appropriate
// TraitsBase specialization.
template <typename T>
class StatusOrData {
template <typename U>
friend class StatusOrData;
public:
StatusOrData() = delete;
StatusOrData(const StatusOrData& other) {
if (other.ok()) {
MakeValue(other.data_);
MakeStatus();
} else {
MakeStatus(other.status_);
}
}
StatusOrData(StatusOrData&& other) noexcept {
if (other.ok()) {
MakeValue(std::move(other.data_));
MakeStatus();
} else {
MakeStatus(std::move(other.status_));
}
}
template <typename U>
explicit StatusOrData(const StatusOrData<U>& other) {
if (other.ok()) {
MakeValue(other.data_);
MakeStatus();
} else {
MakeStatus(other.status_);
}
}
template <typename U>
explicit StatusOrData(StatusOrData<U>&& other) {
if (other.ok()) {
MakeValue(std::move(other.data_));
MakeStatus();
} else {
MakeStatus(std::move(other.status_));
}
}
template <typename... Args>
explicit StatusOrData(absl::in_place_t, Args&&... args)
: data_(std::forward<Args>(args)...) {
MakeStatus();
}
explicit StatusOrData(const T& value) : data_(value) {
MakeStatus();
}
explicit StatusOrData(T&& value) : data_(std::move(value)) {
MakeStatus();
}
template <typename U,
absl::enable_if_t<std::is_constructible<absl::Status, U&&>::value,
int> = 0>
explicit StatusOrData(U&& v) : status_(std::forward<U>(v)) {
EnsureNotOk();
}
StatusOrData& operator=(const StatusOrData& other) {
if (this == &other) return *this;
if (other.ok())
Assign(other.data_);
else
AssignStatus(other.status_);
return *this;
}
StatusOrData& operator=(StatusOrData&& other) {
if (this == &other) return *this;
if (other.ok())
Assign(std::move(other.data_));
else
AssignStatus(std::move(other.status_));
return *this;
}
~StatusOrData() {
if (ok()) {
status_.~Status();
data_.~T();
} else {
status_.~Status();
}
}
template <typename U>
void Assign(U&& value) {
if (ok()) {
data_ = std::forward<U>(value);
} else {
MakeValue(std::forward<U>(value));
status_ = OkStatus();
}
}
template <typename U>
void AssignStatus(U&& v) {
Clear();
status_ = static_cast<absl::Status>(std::forward<U>(v));
EnsureNotOk();
}
bool ok() const { return status_.ok(); }
protected:
// status_ will always be active after the constructor.
// We make it a union to be able to initialize exactly how we need without
// waste.
// Eg. in the copy constructor we use the default constructor of Status in
// the ok() path to avoid an extra Ref call.
union {
Status status_;
};
// data_ is active iff status_.ok()==true
struct Dummy {};
union {
// When T is const, we need some non-const object we can cast to void* for
// the placement new. dummy_ is that object.
Dummy dummy_;
T data_;
};
void Clear() {
if (ok()) data_.~T();
}
void EnsureOk() const {
if (ABSL_PREDICT_FALSE(!ok())) Helper::Crash(status_);
}
void EnsureNotOk() {
if (ABSL_PREDICT_FALSE(ok())) Helper::HandleInvalidStatusCtorArg(&status_);
}
// Construct the value (ie. data_) through placement new with the passed
// argument.
template <typename... Arg>
void MakeValue(Arg&&... arg) {
internal_statusor::PlacementNew<T>(&dummy_, std::forward<Arg>(arg)...);
}
// Construct the status (ie. status_) through placement new with the passed
// argument.
template <typename... Args>
void MakeStatus(Args&&... args) {
internal_statusor::PlacementNew<Status>(&status_,
std::forward<Args>(args)...);
}
};
// Helper base classes to allow implicitly deleted constructors and assignment
// operators in `StatusOr`. For example, `CopyCtorBase` will explicitly delete
// the copy constructor when T is not copy constructible and `StatusOr` will
// inherit that behavior implicitly.
template <typename T, bool = std::is_copy_constructible<T>::value>
struct CopyCtorBase {
CopyCtorBase() = default;
CopyCtorBase(const CopyCtorBase&) = default;
CopyCtorBase(CopyCtorBase&&) = default;
CopyCtorBase& operator=(const CopyCtorBase&) = default;
CopyCtorBase& operator=(CopyCtorBase&&) = default;
};
template <typename T>
struct CopyCtorBase<T, false> {
CopyCtorBase() = default;
CopyCtorBase(const CopyCtorBase&) = delete;
CopyCtorBase(CopyCtorBase&&) = default;
CopyCtorBase& operator=(const CopyCtorBase&) = default;
CopyCtorBase& operator=(CopyCtorBase&&) = default;
};
template <typename T, bool = std::is_move_constructible<T>::value>
struct MoveCtorBase {
MoveCtorBase() = default;
MoveCtorBase(const MoveCtorBase&) = default;
MoveCtorBase(MoveCtorBase&&) = default;
MoveCtorBase& operator=(const MoveCtorBase&) = default;
MoveCtorBase& operator=(MoveCtorBase&&) = default;
};
template <typename T>
struct MoveCtorBase<T, false> {
MoveCtorBase() = default;
MoveCtorBase(const MoveCtorBase&) = default;
MoveCtorBase(MoveCtorBase&&) = delete;
MoveCtorBase& operator=(const MoveCtorBase&) = default;
MoveCtorBase& operator=(MoveCtorBase&&) = default;
};
template <typename T, bool = std::is_copy_constructible<T>::value&&
std::is_copy_assignable<T>::value>
struct CopyAssignBase {
CopyAssignBase() = default;
CopyAssignBase(const CopyAssignBase&) = default;
CopyAssignBase(CopyAssignBase&&) = default;
CopyAssignBase& operator=(const CopyAssignBase&) = default;
CopyAssignBase& operator=(CopyAssignBase&&) = default;
};
template <typename T>
struct CopyAssignBase<T, false> {
CopyAssignBase() = default;
CopyAssignBase(const CopyAssignBase&) = default;
CopyAssignBase(CopyAssignBase&&) = default;
CopyAssignBase& operator=(const CopyAssignBase&) = delete;
CopyAssignBase& operator=(CopyAssignBase&&) = default;
};
template <typename T, bool = std::is_move_constructible<T>::value&&
std::is_move_assignable<T>::value>
struct MoveAssignBase {
MoveAssignBase() = default;
MoveAssignBase(const MoveAssignBase&) = default;
MoveAssignBase(MoveAssignBase&&) = default;
MoveAssignBase& operator=(const MoveAssignBase&) = default;
MoveAssignBase& operator=(MoveAssignBase&&) = default;
};
template <typename T>
struct MoveAssignBase<T, false> {
MoveAssignBase() = default;
MoveAssignBase(const MoveAssignBase&) = default;
MoveAssignBase(MoveAssignBase&&) = default;
MoveAssignBase& operator=(const MoveAssignBase&) = default;
MoveAssignBase& operator=(MoveAssignBase&&) = delete;
};
ABSL_ATTRIBUTE_NORETURN void ThrowBadStatusOrAccess(absl::Status status);
} // namespace internal_statusor
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_STATUS_INTERNAL_STATUSOR_INTERNAL_H_
