2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
19 #include <folly/ExceptionWrapper.h>
20 #include <folly/Likely.h>
21 #include <folly/Memory.h>
22 #include <folly/Portability.h>
23 #include <folly/Unit.h>
26 #include <type_traits>
31 class TryException : public std::logic_error {
33 using std::logic_error::logic_error;
36 class UsingUninitializedTry : public TryException {
38 UsingUninitializedTry() : TryException("Using uninitialized try") {}
42 * Try<T> is a wrapper that contains either an instance of T, an exception, or
43 * nothing. Exceptions are stored as exception_wrappers so that the user can
44 * minimize rethrows if so desired.
46 * To represent success or a captured exception, use Try<Unit>.
50 static_assert(!std::is_reference<T>::value,
51 "Try may not be used with reference types");
61 * The value type for the Try
63 typedef T element_type;
66 * Construct an empty Try
68 Try() : contains_(Contains::NOTHING) {}
71 * Construct a Try with a value by copy
73 * @param v The value to copy in
75 explicit Try(const T& v) : contains_(Contains::VALUE), value_(v) {}
78 * Construct a Try with a value by move
80 * @param v The value to move in
82 explicit Try(T&& v) : contains_(Contains::VALUE), value_(std::move(v)) {}
84 /// Implicit conversion from Try<void> to Try<Unit>
85 template <class T2 = T>
87 Try(typename std::enable_if<std::is_same<Unit, T2>::value,
88 Try<void> const&>::type t);
91 * Construct a Try with an exception_wrapper
93 * @param e The exception_wrapper
95 explicit Try(exception_wrapper e)
96 : contains_(Contains::EXCEPTION), e_(std::move(e)) {}
100 * Construct a Try with an exception_pointer
102 * @param ep The exception_pointer. Will be rethrown.
104 FOLLY_DEPRECATED("use Try(exception_wrapper)")
105 explicit Try(std::exception_ptr ep)
106 : contains_(Contains::EXCEPTION) {
108 std::rethrow_exception(ep);
109 } catch (std::exception& e) {
110 e_ = exception_wrapper(std::current_exception(), e);
112 e_ = exception_wrapper(std::current_exception());
117 Try(Try<T>&& t) noexcept;
119 Try& operator=(Try<T>&& t) noexcept;
124 Try& operator=(const Try& t);
129 * Get a mutable reference to the contained value. If the Try contains an
130 * exception it will be rethrown.
132 * @returns mutable reference to the contained value
136 * Get a rvalue reference to the contained value. If the Try contains an
137 * exception it will be rethrown.
139 * @returns rvalue reference to the contained value
143 * Get a const reference to the contained value. If the Try contains an
144 * exception it will be rethrown.
146 * @returns const reference to the contained value
148 const T& value() const&;
151 * If the Try contains an exception, rethrow it. Otherwise do nothing.
153 void throwIfFailed() const;
156 * Const dereference operator. If the Try contains an exception it will be
159 * @returns const reference to the contained value
161 const T& operator*() const { return value(); }
163 * Dereference operator. If the Try contains an exception it will be rethrown.
165 * @returns mutable reference to the contained value
167 T& operator*() { return value(); }
170 * Const arrow operator. If the Try contains an exception it will be
173 * @returns const reference to the contained value
175 const T* operator->() const { return &value(); }
177 * Arrow operator. If the Try contains an exception it will be rethrown.
179 * @returns mutable reference to the contained value
181 T* operator->() { return &value(); }
184 * @returns True if the Try contains a value, false otherwise
186 bool hasValue() const { return contains_ == Contains::VALUE; }
188 * @returns True if the Try contains an exception, false otherwise
190 bool hasException() const { return contains_ == Contains::EXCEPTION; }
193 * @returns True if the Try contains an exception of type Ex, false otherwise
196 bool hasException() const {
197 return hasException() && e_.is_compatible_with<Ex>();
200 exception_wrapper& exception() {
201 if (UNLIKELY(!hasException())) {
202 throw TryException("exception(): Try does not contain an exception");
207 const exception_wrapper& exception() const {
208 if (UNLIKELY(!hasException())) {
209 throw TryException("exception(): Try does not contain an exception");
215 * If the Try contains an exception and it is of type Ex, execute func(Ex)
217 * @param func a function that takes a single parameter of type const Ex&
219 * @returns True if the Try held an Ex and func was executed, false otherwise
221 template <class Ex, class F>
222 bool withException(F func) {
223 if (!hasException()) {
226 return e_.with_exception(std::move(func));
228 template <class Ex, class F>
229 bool withException(F func) const {
230 if (!hasException()) {
233 return e_.with_exception(std::move(func));
236 template <bool isTry, typename R>
237 typename std::enable_if<isTry, R>::type get() {
238 return std::forward<R>(*this);
241 template <bool isTry, typename R>
242 typename std::enable_if<!isTry, R>::type get() {
243 return std::forward<R>(value());
250 exception_wrapper e_;
255 * Specialization of Try for void value type. Encapsulates either success or an
262 * The value type for the Try
264 typedef void element_type;
266 // Construct a Try holding a successful and void result
267 Try() : hasValue_(true) {}
270 * Construct a Try with an exception_wrapper
272 * @param e The exception_wrapper
274 explicit Try(exception_wrapper e) : hasValue_(false), e_(std::move(e)) {}
278 * Construct a Try with an exception_pointer
280 * @param ep The exception_pointer. Will be rethrown.
282 FOLLY_DEPRECATED("use Try(exception_wrapper)")
283 explicit Try(std::exception_ptr ep) : hasValue_(false) {
285 std::rethrow_exception(ep);
286 } catch (const std::exception& e) {
287 e_ = exception_wrapper(std::current_exception(), e);
289 e_ = exception_wrapper(std::current_exception());
294 Try& operator=(const Try<void>& t) {
295 hasValue_ = t.hasValue_;
300 Try(const Try<void>& t) {
304 // If the Try contains an exception, throws it
305 void value() const { throwIfFailed(); }
306 // Dereference operator. If the Try contains an exception, throws it
307 void operator*() const { return value(); }
309 // If the Try contains an exception, throws it
310 inline void throwIfFailed() const;
312 // @returns False if the Try contains an exception, true otherwise
313 bool hasValue() const { return hasValue_; }
314 // @returns True if the Try contains an exception, false otherwise
315 bool hasException() const { return !hasValue_; }
317 // @returns True if the Try contains an exception of type Ex, false otherwise
319 bool hasException() const {
320 return hasException() && e_.is_compatible_with<Ex>();
324 * @throws TryException if the Try doesn't contain an exception
326 * @returns mutable reference to the exception contained by this Try
328 exception_wrapper& exception() {
329 if (UNLIKELY(!hasException())) {
330 throw TryException("exception(): Try does not contain an exception");
335 const exception_wrapper& exception() const {
336 if (UNLIKELY(!hasException())) {
337 throw TryException("exception(): Try does not contain an exception");
343 * If the Try contains an exception and it is of type Ex, execute func(Ex)
345 * @param func a function that takes a single parameter of type const Ex&
347 * @returns True if the Try held an Ex and func was executed, false otherwise
349 template <class Ex, class F>
350 bool withException(F func) {
351 if (!hasException()) {
354 return e_.with_exception(std::move(func));
356 template <class Ex, class F>
357 bool withException(F func) const {
358 if (!hasException()) {
361 return e_.with_exception(std::move(func));
364 template <bool, typename R>
366 return std::forward<R>(*this);
371 exception_wrapper e_;
375 * Extracts value from try and returns it. Throws if try contained an exception.
377 * @param t Try to extract value from
379 * @returns value contained in t
381 template <typename T>
382 T moveFromTry(Try<T>& t);
385 * Throws if try contained an exception.
387 * @param t Try to move from
389 void moveFromTry(Try<void>& t);
392 * @param f a function to execute and capture the result of (value or exception)
394 * @returns Try holding the result of f
396 template <typename F>
397 typename std::enable_if<
398 !std::is_same<typename std::result_of<F()>::type, void>::value,
399 Try<typename std::result_of<F()>::type>>::type
403 * Specialization of makeTryWith for void return
405 * @param f a function to execute and capture the result of
407 * @returns Try<void> holding the result of f
409 template <typename F>
410 typename std::enable_if<
411 std::is_same<typename std::result_of<F()>::type, void>::value,
415 template <typename... Ts>
416 std::tuple<Ts...> unwrapTryTuple(std::tuple<folly::Try<Ts>...>&& ts);
420 #include <folly/Try-inl.h>