namespace folly {
+template <class Value>
+class Optional;
+
namespace detail {
struct NoneHelper {};
// If exceptions are disabled, std::terminate() will be called instead of
// throwing OptionalEmptyException when the condition fails.
[[noreturn]] void throw_optional_empty_exception();
-}
+
+template <class Value>
+struct OptionalPromiseReturn;
+} // namespace detail
typedef int detail::NoneHelper::*None;
!std::is_abstract<Value>::value,
"Optional may not be used with abstract types");
- Optional() noexcept {}
+ FOLLY_CPP14_CONSTEXPR Optional() noexcept {}
Optional(const Optional& src) noexcept(
std::is_nothrow_copy_constructible<Value>::value) {
}
}
- /* implicit */ Optional(const None&) noexcept {}
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(const None&) noexcept {}
- /* implicit */ Optional(Value&& newValue) noexcept(
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(Value&& newValue) noexcept(
std::is_nothrow_move_constructible<Value>::value) {
storage_.construct(std::move(newValue));
}
- /* implicit */ Optional(const Value& newValue) noexcept(
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(const Value& newValue) noexcept(
std::is_nothrow_copy_constructible<Value>::value) {
storage_.construct(newValue);
}
template <typename... Args>
- explicit Optional(in_place_t, Args&&... args) noexcept(
+ FOLLY_CPP14_CONSTEXPR explicit Optional(in_place_t, Args&&... args) noexcept(
std::is_nothrow_constructible<Value, Args...>::value) {
storage_.construct(std::forward<Args>(args)...);
}
+ // Used only when an Optional is used with coroutines on MSVC
+ /* implicit */ Optional(const detail::OptionalPromiseReturn<Value>& p)
+ : Optional{} {
+ p.promise_->value_ = this;
+ }
+
void assign(const None&) {
clear();
}
storage_.clear();
}
- const Value& value() const & {
+ FOLLY_CPP14_CONSTEXPR const Value& value() const & {
require_value();
return *storage_.value_pointer();
}
- Value& value() & {
+ FOLLY_CPP14_CONSTEXPR Value& value() & {
require_value();
return *storage_.value_pointer();
}
- Value&& value() && {
+ FOLLY_CPP14_CONSTEXPR Value&& value() && {
require_value();
return std::move(*storage_.value_pointer());
}
- const Value&& value() const && {
+ FOLLY_CPP14_CONSTEXPR const Value&& value() const && {
require_value();
return std::move(*storage_.value_pointer());
}
}
Value* get_pointer() && = delete;
- bool hasValue() const {
+ FOLLY_CPP14_CONSTEXPR bool hasValue() const noexcept {
return storage_.hasValue();
}
- explicit operator bool() const {
+ FOLLY_CPP14_CONSTEXPR explicit operator bool() const noexcept {
return hasValue();
}
- const Value& operator*() const & {
+ FOLLY_CPP14_CONSTEXPR const Value& operator*() const & {
return value();
}
- Value& operator*() & {
+ FOLLY_CPP14_CONSTEXPR Value& operator*() & {
return value();
}
- const Value&& operator*() const && {
+ FOLLY_CPP14_CONSTEXPR const Value&& operator*() const && {
return std::move(value());
}
- Value&& operator*() && {
+ FOLLY_CPP14_CONSTEXPR Value&& operator*() && {
return std::move(value());
}
- const Value* operator->() const {
+ FOLLY_CPP14_CONSTEXPR const Value* operator->() const {
return &value();
}
- Value* operator->() {
+ FOLLY_CPP14_CONSTEXPR Value* operator->() {
return &value();
}
// Return a copy of the value if set, or a given default if not.
template <class U>
- Value value_or(U&& dflt) const & {
+ FOLLY_CPP14_CONSTEXPR Value value_or(U&& dflt) const & {
if (storage_.hasValue()) {
return *storage_.value_pointer();
}
}
template <class U>
- Value value_or(U&& dflt) && {
+ FOLLY_CPP14_CONSTEXPR Value value_or(U&& dflt) && {
if (storage_.hasValue()) {
return std::move(*storage_.value_pointer());
}
std::is_trivially_destructible<Value>::value,
StorageTriviallyDestructible,
StorageNonTriviallyDestructible>::type {
- bool hasValue() const {
+ bool hasValue() const noexcept {
return this->hasValue_;
}
}
template <class T, class Opt = Optional<typename std::decay<T>::type>>
-Opt make_optional(T&& v) {
+constexpr Opt make_optional(T&& v) {
return Opt(std::forward<T>(v));
}
// Comparisons.
template <class U, class V>
-bool operator==(const Optional<U>& a, const V& b) {
+constexpr bool operator==(const Optional<U>& a, const V& b) {
return a.hasValue() && a.value() == b;
}
template <class U, class V>
-bool operator!=(const Optional<U>& a, const V& b) {
+constexpr bool operator!=(const Optional<U>& a, const V& b) {
return !(a == b);
}
template <class U, class V>
-bool operator==(const U& a, const Optional<V>& b) {
+constexpr bool operator==(const U& a, const Optional<V>& b) {
return b.hasValue() && b.value() == a;
}
template <class U, class V>
-bool operator!=(const U& a, const Optional<V>& b) {
+constexpr bool operator!=(const U& a, const Optional<V>& b) {
return !(a == b);
}
template <class U, class V>
-bool operator==(const Optional<U>& a, const Optional<V>& b) {
+FOLLY_CPP14_CONSTEXPR bool operator==(
+ const Optional<U>& a,
+ const Optional<V>& b) {
if (a.hasValue() != b.hasValue()) {
return false;
}
}
template <class U, class V>
-bool operator!=(const Optional<U>& a, const Optional<V>& b) {
+constexpr bool operator!=(const Optional<U>& a, const Optional<V>& b) {
return !(a == b);
}
template <class U, class V>
-bool operator<(const Optional<U>& a, const Optional<V>& b) {
+FOLLY_CPP14_CONSTEXPR bool operator<(
+ const Optional<U>& a,
+ const Optional<V>& b) {
if (a.hasValue() != b.hasValue()) {
return a.hasValue() < b.hasValue();
}
}
template <class U, class V>
-bool operator>(const Optional<U>& a, const Optional<V>& b) {
+constexpr bool operator>(const Optional<U>& a, const Optional<V>& b) {
return b < a;
}
template <class U, class V>
-bool operator<=(const Optional<U>& a, const Optional<V>& b) {
+constexpr bool operator<=(const Optional<U>& a, const Optional<V>& b) {
return !(b < a);
}
template <class U, class V>
-bool operator>=(const Optional<U>& a, const Optional<V>& b) {
+constexpr bool operator>=(const Optional<U>& a, const Optional<V>& b) {
return !(a < b);
}
template <class V>
bool operator>(const V& other, const Optional<V>&) = delete;
+// Comparisons with none
+template <class V>
+constexpr bool operator==(const Optional<V>& a, None) noexcept {
+ return !a.hasValue();
+}
+template <class V>
+constexpr bool operator==(None, const Optional<V>& a) noexcept {
+ return !a.hasValue();
+}
+template <class V>
+constexpr bool operator<(const Optional<V>&, None) noexcept {
+ return false;
+}
+template <class V>
+constexpr bool operator<(None, const Optional<V>& a) noexcept {
+ return a.hasValue();
+}
+template <class V>
+constexpr bool operator>(const Optional<V>& a, None) noexcept {
+ return a.hasValue();
+}
+template <class V>
+constexpr bool operator>(None, const Optional<V>&) noexcept {
+ return false;
+}
+template <class V>
+constexpr bool operator<=(None, const Optional<V>&) noexcept {
+ return true;
+}
+template <class V>
+constexpr bool operator<=(const Optional<V>& a, None) noexcept {
+ return !a.hasValue();
+}
+template <class V>
+constexpr bool operator>=(const Optional<V>&, None) noexcept {
+ return true;
+}
+template <class V>
+constexpr bool operator>=(None, const Optional<V>& a) noexcept {
+ return !a.hasValue();
+}
+
///////////////////////////////////////////////////////////////////////////////
} // namespace folly
}
};
FOLLY_NAMESPACE_STD_END
+
+// Enable the use of folly::Optional with `co_await`
+// Inspired by https://github.com/toby-allsopp/coroutine_monad
+#if FOLLY_HAS_COROUTINES
+#include <experimental/coroutine>
+
+namespace folly {
+namespace detail {
+template <typename Value>
+struct OptionalPromise;
+
+template <typename Value>
+struct OptionalPromiseReturn {
+ Optional<Value> storage_;
+ OptionalPromise<Value>* promise_;
+ /* implicit */ OptionalPromiseReturn(OptionalPromise<Value>& promise) noexcept
+ : promise_(&promise) {
+ promise.value_ = &storage_;
+ }
+ OptionalPromiseReturn(OptionalPromiseReturn&& that) noexcept
+ : OptionalPromiseReturn{*that.promise_} {}
+ ~OptionalPromiseReturn() {}
+ /* implicit */ operator Optional<Value>() & {
+ return std::move(storage_);
+ }
+};
+
+template <typename Value>
+struct OptionalPromise {
+ Optional<Value>* value_ = nullptr;
+ OptionalPromise() = default;
+ OptionalPromise(OptionalPromise const&) = delete;
+ // This should work regardless of whether the compiler generates:
+ // folly::Optional<Value> retobj{ p.get_return_object(); } // MSVC
+ // or:
+ // auto retobj = p.get_return_object(); // clang
+ OptionalPromiseReturn<Value> 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_ = 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>
+struct OptionalAwaitable {
+ Optional<Value> o_;
+ bool await_ready() const noexcept {
+ return o_.hasValue();
+ }
+ Value await_resume() {
+ return std::move(o_.value());
+ }
+
+ // Explicitly only allow suspension into an OptionalPromise
+ template <typename U>
+ void await_suspend(
+ std::experimental::coroutine_handle<OptionalPromise<U>> h) const {
+ // Abort the rest of the coroutine. resume() is not going to be called
+ h.destroy();
+ }
+};
+} // namespace detail
+
+template <typename Value>
+detail::OptionalAwaitable<Value>
+/* implicit */ operator co_await(Optional<Value> o) {
+ return {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... Args>
+struct coroutine_traits<folly::Optional<Value>, Args...> {
+ using promise_type = folly::detail::OptionalPromise<Value>;
+};
+} // experimental
+FOLLY_NAMESPACE_STD_END
+#endif // FOLLY_HAS_COROUTINES
projects / folly.git / blobdiff