1 //===- llvm/Support/ErrorOr.h - Error Smart Pointer -----------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
12 /// Provides ErrorOr<T> smart pointer.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_SUPPORT_ERROR_OR_H
17 #define LLVM_SUPPORT_ERROR_OR_H
19 #include "llvm/ADT/PointerIntPair.h"
20 #include "llvm/Support/AlignOf.h"
21 #include "llvm/Support/system_error.h"
22 #include "llvm/Support/type_traits.h"
24 #if LLVM_HAS_CXX11_TYPETRAITS
25 #include <type_traits>
29 #if LLVM_HAS_CXX11_TYPETRAITS && LLVM_HAS_RVALUE_REFERENCES
30 template<class T, class V>
31 typename std::enable_if< std::is_constructible<T, V>::value
32 , typename std::remove_reference<V>::type>::type &&
33 moveIfMoveConstructible(V &Val) {
34 return std::move(Val);
37 template<class T, class V>
38 typename std::enable_if< !std::is_constructible<T, V>::value
39 , typename std::remove_reference<V>::type>::type &
40 moveIfMoveConstructible(V &Val) {
44 template<class T, class V>
45 V &moveIfMoveConstructible(V &Val) {
50 /// \brief Stores a reference that can be changed.
52 class ReferenceStorage {
56 ReferenceStorage(T &Ref) : Storage(&Ref) {}
58 operator T &() const { return *Storage; }
59 T &get() const { return *Storage; }
62 /// \brief Represents either an error or a value T.
64 /// ErrorOr<T> is a pointer-like class that represents the result of an
65 /// operation. The result is either an error, or a value of type T. This is
66 /// designed to emulate the usage of returning a pointer where nullptr indicates
67 /// failure. However instead of just knowing that the operation failed, we also
68 /// have an error_code and optional user data that describes why it failed.
70 /// It is used like the following.
72 /// ErrorOr<Buffer> getBuffer();
74 /// auto buffer = getBuffer();
75 /// if (error_code ec = buffer.getError())
77 /// buffer->write("adena");
81 /// An implicit conversion to bool provides a way to check if there was an
82 /// error. The unary * and -> operators provide pointer like access to the
83 /// value. Accessing the value when there is an error has undefined behavior.
85 /// When T is a reference type the behaivor is slightly different. The reference
86 /// is held in a std::reference_wrapper<std::remove_reference<T>::type>, and
87 /// there is special handling to make operator -> work as if T was not a
90 /// T cannot be a rvalue reference.
93 template <class OtherT> friend class ErrorOr;
94 static const bool isRef = is_reference<T>::value;
95 typedef ReferenceStorage<typename remove_reference<T>::type> wrap;
102 >::type storage_type;
105 typedef typename remove_reference<T>::type &reference;
106 typedef typename remove_reference<T>::type *pointer;
110 ErrorOr(E ErrorCode, typename enable_if_c<is_error_code_enum<E>::value ||
111 is_error_condition_enum<E>::value,
114 new (getErrorStorage()) error_code(make_error_code(ErrorCode));
117 ErrorOr(llvm::error_code EC) : HasError(true) {
118 new (getErrorStorage()) error_code(EC);
121 ErrorOr(T Val) : HasError(false) {
122 new (getStorage()) storage_type(moveIfMoveConstructible<storage_type>(Val));
125 ErrorOr(const ErrorOr &Other) {
126 copyConstruct(Other);
129 template <class OtherT>
130 ErrorOr(const ErrorOr<OtherT> &Other) {
131 copyConstruct(Other);
134 ErrorOr &operator =(const ErrorOr &Other) {
139 template <class OtherT>
140 ErrorOr &operator =(const ErrorOr<OtherT> &Other) {
145 #if LLVM_HAS_RVALUE_REFERENCES
146 ErrorOr(ErrorOr &&Other) {
147 moveConstruct(std::move(Other));
150 template <class OtherT>
151 ErrorOr(ErrorOr<OtherT> &&Other) {
152 moveConstruct(std::move(Other));
155 ErrorOr &operator =(ErrorOr &&Other) {
156 moveAssign(std::move(Other));
160 template <class OtherT>
161 ErrorOr &operator =(ErrorOr<OtherT> &&Other) {
162 moveAssign(std::move(Other));
169 getStorage()->~storage_type();
172 /// \brief Return false if there is an error.
173 LLVM_EXPLICIT operator bool() const {
177 reference get() { return *getStorage(); }
178 const reference get() const { return const_cast<ErrorOr<T> >(this)->get(); }
180 error_code getError() const {
181 return HasError ? *getErrorStorage() : error_code::success();
184 pointer operator ->() {
185 return toPointer(getStorage());
188 reference operator *() {
189 return *getStorage();
193 template <class OtherT>
194 void copyConstruct(const ErrorOr<OtherT> &Other) {
195 if (!Other.HasError) {
196 // Get the other value.
198 new (getStorage()) storage_type(*Other.getStorage());
200 // Get other's error.
202 new (getErrorStorage()) error_code(Other.getError());
207 static bool compareThisIfSameType(const T1 &a, const T1 &b) {
211 template <class T1, class T2>
212 static bool compareThisIfSameType(const T1 &a, const T2 &b) {
216 template <class OtherT>
217 void copyAssign(const ErrorOr<OtherT> &Other) {
218 if (compareThisIfSameType(*this, Other))
222 new (this) ErrorOr(Other);
225 #if LLVM_HAS_RVALUE_REFERENCES
226 template <class OtherT>
227 void moveConstruct(ErrorOr<OtherT> &&Other) {
228 if (!Other.HasError) {
229 // Get the other value.
231 new (getStorage()) storage_type(std::move(*Other.getStorage()));
233 // Get other's error.
235 new (getErrorStorage()) error_code(Other.getError());
239 template <class OtherT>
240 void moveAssign(ErrorOr<OtherT> &&Other) {
241 if (compareThisIfSameType(*this, Other))
245 new (this) ErrorOr(std::move(Other));
249 pointer toPointer(pointer Val) {
253 pointer toPointer(wrap *Val) {
257 storage_type *getStorage() {
258 assert(!HasError && "Cannot get value when an error exists!");
259 return reinterpret_cast<storage_type*>(TStorage.buffer);
262 const storage_type *getStorage() const {
263 assert(!HasError && "Cannot get value when an error exists!");
264 return reinterpret_cast<const storage_type*>(TStorage.buffer);
267 error_code *getErrorStorage() {
268 assert(HasError && "Cannot get error when a value exists!");
269 return reinterpret_cast<error_code*>(ErrorStorage.buffer);
272 const error_code *getErrorStorage() const {
273 return const_cast<ErrorOr<T> *>(this)->getErrorStorage();
278 AlignedCharArrayUnion<storage_type> TStorage;
279 AlignedCharArrayUnion<error_code> ErrorStorage;
284 template<class T, class E>
285 typename enable_if_c<is_error_code_enum<E>::value ||
286 is_error_condition_enum<E>::value, bool>::type
287 operator ==(ErrorOr<T> &Err, E Code) {
288 return error_code(Err) == Code;
290 } // end namespace llvm