#include <type_traits>
#include <utility>
+#include <glog/logging.h>
+
#include <folly/Likely.h>
+#include <folly/Optional.h>
#include <folly/Portability.h>
#include <folly/Preprocessor.h>
#include <folly/Traits.h>
// Details...
namespace expected_detail {
+
+template <typename Value, typename Error>
+struct PromiseReturn;
+
#ifdef _MSC_VER
// MSVC 2015 can't handle the StrictConjunction, so we have
// to use std::conjunction instead.
return *this;
}
+ // Used only when an Expected is used with coroutines on MSVC
+ /* implicit */ Expected(const expected_detail::PromiseReturn<Value, Error>& p)
+ : Expected{} {
+ p.promise_->value_ = this;
+ }
+
template <class... Ts FOLLY_REQUIRES_TRAILING(
std::is_constructible<Value, Ts&&...>::value)>
void emplace(Ts&&... ts) {
#undef FOLLY_REQUIRES
#undef FOLLY_REQUIRES_TRAILING
+
+// Enable the use of folly::Expected with `co_await`
+// Inspired by https://github.com/toby-allsopp/coroutine_monad
+#if FOLLY_HAS_COROUTINES
+#include <experimental/coroutine>
+
+namespace folly {
+namespace expected_detail {
+template <typename Value, typename Error>
+struct Promise;
+
+template <typename Value, typename Error>
+struct PromiseReturn {
+ Optional<Expected<Value, Error>> storage_;
+ Promise<Value, Error>* promise_;
+ /* implicit */ PromiseReturn(Promise<Value, Error>& promise) noexcept
+ : promise_(&promise) {
+ promise_->value_ = &storage_;
+ }
+ PromiseReturn(PromiseReturn&& that) noexcept
+ : PromiseReturn{*that.promise_} {}
+ ~PromiseReturn() {}
+ /* implicit */ operator Expected<Value, Error>() & {
+ return std::move(*storage_);
+ }
+};
+
+template <typename Value, typename Error>
+struct Promise {
+ Optional<Expected<Value, Error>>* value_ = nullptr;
+ Promise() = default;
+ Promise(Promise const&) = delete;
+ // This should work regardless of whether the compiler generates:
+ // folly::Expected<Value, Error> retobj{ p.get_return_object(); } // MSVC
+ // or:
+ // auto retobj = p.get_return_object(); // clang
+ PromiseReturn<Value, Error> get_return_object() noexcept {
+ return *this;
+ }
+ std::experimental::suspend_never initial_suspend() const noexcept {
+ return {};
+ }
+ std::experimental::suspend_never final_suspend() const {
+ return {};
+ }
+ template <typename U>
+ void return_value(U&& u) {
+ value_->emplace(static_cast<U&&>(u));
+ }
+ void unhandled_exception() {
+ // Technically, throwing from unhandled_exception is underspecified:
+ // https://github.com/GorNishanov/CoroutineWording/issues/17
+ throw;
+ }
+};
+
+template <typename Value, typename Error>
+struct Awaitable {
+ Expected<Value, Error> o_;
+
+ explicit Awaitable(Expected<Value, Error> o) : o_(std::move(o)) {}
+
+ bool await_ready() const noexcept {
+ return o_.hasValue();
+ }
+ Value await_resume() {
+ return std::move(o_.value());
+ }
+
+ // Explicitly only allow suspension into a Promise
+ template <typename U>
+ void await_suspend(std::experimental::coroutine_handle<Promise<U, Error>> h) {
+ *h.promise().value_ = makeUnexpected(std::move(o_.error()));
+ // Abort the rest of the coroutine. resume() is not going to be called
+ h.destroy();
+ }
+};
+} // namespace expected_detail
+
+template <typename Value, typename Error>
+expected_detail::Awaitable<Value, Error>
+/* implicit */ operator co_await(Expected<Value, Error> o) {
+ return expected_detail::Awaitable<Value, Error>{std::move(o)};
+}
+} // namespace folly
+
+// This makes folly::Optional<Value> useable as a coroutine return type..
+FOLLY_NAMESPACE_STD_BEGIN
+namespace experimental {
+template <typename Value, typename Error, typename... Args>
+struct coroutine_traits<folly::Expected<Value, Error>, Args...> {
+ using promise_type = folly::expected_detail::Promise<Value, Error>;
+};
+} // namespace experimental
+FOLLY_NAMESPACE_STD_END
+#endif // FOLLY_HAS_COROUTINES
--- /dev/null
+/*
+ * Copyright 2017 Facebook, Inc.
+ *
+ * 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
+ *
+ * http://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.
+ */
+
+#include <folly/Expected.h>
+#include <folly/Portability.h>
+#include <folly/ScopeGuard.h>
+#include <folly/portability/GTest.h>
+
+using namespace folly;
+
+namespace {
+
+struct Exn {};
+
+// not default-constructible, thereby preventing Expected<T, Err> from being
+// default-constructible, forcing our implementation to handle such cases
+class Err {
+ private:
+ enum class Type { Bad, Badder, Baddest };
+
+ Type type_;
+
+ constexpr Err(Type type) : type_(type) {}
+
+ public:
+ Err(Err const&) = default;
+ Err(Err&&) = default;
+ Err& operator=(Err const&) = default;
+ Err& operator=(Err&&) = default;
+
+ friend bool operator==(Err a, Err b) {
+ return a.type_ == b.type_;
+ }
+ friend bool operator!=(Err a, Err b) {
+ return a.type_ != b.type_;
+ }
+
+ static constexpr Err bad() {
+ return Type::Bad;
+ }
+ static constexpr Err badder() {
+ return Type::Badder;
+ }
+ static constexpr Err baddest() {
+ return Type::Baddest;
+ }
+};
+
+Expected<int, Err> f1() {
+ return 7;
+}
+
+Expected<double, Err> f2(int x) {
+ return 2.0 * x;
+}
+
+// move-only type
+Expected<std::unique_ptr<int>, Err> f3(int x, double y) {
+ return std::make_unique<int>(int(x + y));
+}
+
+// error result
+Expected<int, Err> f4(int, double, Err err) {
+ return makeUnexpected(err);
+}
+
+// exception
+Expected<int, Err> throws() {
+ throw Exn{};
+}
+
+} // namespace
+
+#if FOLLY_HAS_COROUTINES
+
+TEST(Expected, CoroutineSuccess) {
+ auto r0 = []() -> Expected<int, Err> {
+ auto x = co_await f1();
+ EXPECT_EQ(7, x);
+ auto y = co_await f2(x);
+ EXPECT_EQ(2.0 * 7, y);
+ auto z = co_await f3(x, y);
+ EXPECT_EQ(int(2.0 * 7 + 7), *z);
+ co_return* z;
+ }();
+ EXPECT_TRUE(r0.hasValue());
+ EXPECT_EQ(21, *r0);
+}
+
+TEST(Expected, CoroutineFailure) {
+ auto r1 = []() -> Expected<int, Err> {
+ auto x = co_await f1();
+ auto y = co_await f2(x);
+ auto z = co_await f4(x, y, Err::badder());
+ ADD_FAILURE();
+ co_return z;
+ }();
+ EXPECT_TRUE(r1.hasError());
+ EXPECT_EQ(Err::badder(), r1.error());
+}
+
+TEST(Expected, CoroutineException) {
+ EXPECT_THROW(
+ ([]() -> Expected<int, Err> {
+ auto x = co_await throws();
+ ADD_FAILURE();
+ co_return x;
+ }()),
+ Exn);
+}
+
+// this test makes sure that the coroutine is destroyed properly
+TEST(Expected, CoroutineCleanedUp) {
+ int count_dest = 0;
+ auto r = [&]() -> Expected<int, Err> {
+ SCOPE_EXIT {
+ ++count_dest;
+ };
+ auto x = co_await Expected<int, Err>(makeUnexpected(Err::badder()));
+ ADD_FAILURE() << "Should not be resuming";
+ co_return x;
+ }();
+ EXPECT_FALSE(r.hasValue());
+ EXPECT_EQ(1, count_dest);
+}
+
+#endif
projects / folly.git / commitdiff