* cout << *v << endl;
* }
*/
+
#include <cstddef>
#include <functional>
#include <new>
#include <type_traits>
#include <utility>
+#include <folly/Launder.h>
#include <folly/Portability.h>
+#include <folly/Traits.h>
#include <folly/Utility.h>
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) {
if (src.hasValue()) {
- construct(src.value());
+ storage_.construct(src.value());
}
}
Optional(Optional&& src) noexcept(
std::is_nothrow_move_constructible<Value>::value) {
if (src.hasValue()) {
- construct(std::move(src.value()));
+ storage_.construct(std::move(src.value()));
src.clear();
}
}
- /* 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) {
- construct(std::move(newValue));
+ 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) {
- construct(newValue);
+ 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) {
- construct(std::forward<Args>(args)...);
+ 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&) {
void assign(Value&& newValue) {
if (hasValue()) {
- storage_.value = std::move(newValue);
+ *storage_.value_pointer() = std::move(newValue);
} else {
- construct(std::move(newValue));
+ storage_.construct(std::move(newValue));
}
}
void assign(const Value& newValue) {
if (hasValue()) {
- storage_.value = newValue;
+ *storage_.value_pointer() = newValue;
} else {
- construct(newValue);
+ storage_.construct(newValue);
}
}
}
template <class... Args>
- void emplace(Args&&... args) {
+ Value& emplace(Args&&... args) {
+ clear();
+ return storage_.construct(std::forward<Args>(args)...);
+ }
+
+ template <class U, class... Args>
+ typename std::enable_if<
+ std::is_constructible<Value, std::initializer_list<U>&, Args&&...>::value,
+ Value&>::type
+ emplace(std::initializer_list<U> ilist, Args&&... args) {
clear();
-
construct(std::forward<Args>(args)...);
+
return storage_.construct(ilist, std::forward<Args>(args)...);
}
- void clear() {
+ void reset() noexcept {
storage_.clear();
}
- const Value& value() const & {
+ void clear() noexcept {
+ reset();
+ }
+
+ void swap(Optional& that) noexcept(IsNothrowSwappable<Value>::value) {
+ if (hasValue() && that.hasValue()) {
+ using std::swap;
+ swap(value(), that.value());
+ } else if (hasValue()) {
+ that.emplace(std::move(value()));
+ reset();
+ } else if (that.hasValue()) {
+ emplace(std::move(that.value()));
+ that.reset();
+ }
+ }
+
+ FOLLY_CPP14_CONSTEXPR const Value& value() const & {
require_value();
- return storage_.value;
+ return *storage_.value_pointer();
}
- Value& value() & {
+ FOLLY_CPP14_CONSTEXPR Value& value() & {
require_value();
- return storage_.value;
+ return *storage_.value_pointer();
}
- Value&& value() && {
+ FOLLY_CPP14_CONSTEXPR Value&& value() && {
require_value();
- return std::move(storage_.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);
+ return std::move(*storage_.value_pointer());
}
const Value* get_pointer() const & {
- return storage_.hasValue ? &storage_.value : nullptr;
+ return storage_.value_pointer();
}
Value* get_pointer() & {
- return storage_.hasValue ? &storage_.value : nullptr;
+ return storage_.value_pointer();
}
Value* get_pointer() && = delete;
- bool hasValue() const {
- return storage_.hasValue;
+ FOLLY_CPP14_CONSTEXPR bool has_value() const noexcept {
+ return storage_.hasValue();
}
- explicit operator bool() const {
- return hasValue();
+ FOLLY_CPP14_CONSTEXPR bool hasValue() const noexcept {
+ return has_value();
}
- const Value& operator*() const & {
+ FOLLY_CPP14_CONSTEXPR explicit operator bool() const noexcept {
+ return has_value();
+ }
+
+ 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 & {
- if (storage_.hasValue) {
- return storage_.value;
+ FOLLY_CPP14_CONSTEXPR Value value_or(U&& dflt) const & {
+ if (storage_.hasValue()) {
+ return *storage_.value_pointer();
}
return std::forward<U>(dflt);
}
template <class U>
- Value value_or(U&& dflt) && {
- if (storage_.hasValue) {
- return std::move(storage_.value);
+ FOLLY_CPP14_CONSTEXPR Value value_or(U&& dflt) && {
+ if (storage_.hasValue()) {
+ return std::move(*storage_.value_pointer());
}
return std::forward<U>(dflt);
private:
void require_value() const {
- if (!storage_.hasValue) {
+ if (!storage_.hasValue()) {
detail::throw_optional_empty_exception();
}
}
- template <class... Args>
- void construct(Args&&... args) {
- const void* ptr = &storage_.value;
- // for supporting const types
- new (const_cast<void*>(ptr)) Value(std::forward<Args>(args)...);
- storage_.hasValue = true;
- }
-
struct StorageTriviallyDestructible {
- // The union trick allows to initialize the Optional's memory,
- // so that compiler/tools don't complain about uninitialized memory,
- // without actually calling Value's default constructor.
- // The rest of the implementation enforces that hasValue/value are
- // synchronized.
- union {
- bool hasValue;
- struct {
- bool paddingForHasValue_[1];
- Value value;
- };
- };
-
- StorageTriviallyDestructible() : hasValue{false} {}
+ protected:
+ bool hasValue_;
+ typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+ value_[1];
+ public:
+ StorageTriviallyDestructible() : hasValue_{false} {}
void clear() {
- hasValue = false;
+ hasValue_ = false;
}
};
struct StorageNonTriviallyDestructible {
- // See StorageTriviallyDestructible's union
- union {
- bool hasValue;
- struct {
- bool paddingForHasValue_[1];
- Value value;
- };
- };
-
- FOLLY_PUSH_WARNING
- // These are both informational warnings, but they trigger rare enough
- // that we've left them enabled.
- FOLLY_MSVC_DISABLE_WARNING(4587) // constructor of .value is not called
- FOLLY_MSVC_DISABLE_WARNING(4588) // destructor of .value is not called
- StorageNonTriviallyDestructible() : hasValue{false} {}
+ protected:
+ bool hasValue_;
+ typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+ value_[1];
+
+ public:
+ StorageNonTriviallyDestructible() : hasValue_{false} {}
~StorageNonTriviallyDestructible() {
clear();
}
- FOLLY_POP_WARNING
void clear() {
- if (hasValue) {
- hasValue = false;
- value.~Value();
+ if (hasValue_) {
+ hasValue_ = false;
+ launder(reinterpret_cast<Value*>(value_))->~Value();
}
}
};
- using Storage = typename std::conditional<
- std::is_trivially_destructible<Value>::value,
- StorageTriviallyDestructible,
- StorageNonTriviallyDestructible>::type;
+ struct Storage : std::conditional<
+ std::is_trivially_destructible<Value>::value,
+ StorageTriviallyDestructible,
+ StorageNonTriviallyDestructible>::type {
+ bool hasValue() const noexcept {
+ return this->hasValue_;
+ }
+
+ Value* value_pointer() {
+ if (this->hasValue_) {
+ return launder(reinterpret_cast<Value*>(this->value_));
+ }
+ return nullptr;
+ }
+
+ Value const* value_pointer() const {
+ if (this->hasValue_) {
+ return launder(reinterpret_cast<Value const*>(this->value_));
+ }
+ return nullptr;
+ }
+
+ template <class... Args>
+ Value& construct(Args&&... args) {
+ new (raw_pointer()) Value(std::forward<Args>(args)...);
+ this->hasValue_ = true;
+ return *launder(reinterpret_cast<Value*>(this->value_));
+ }
+
+ private:
+ void* raw_pointer() {
+ return static_cast<void*>(this->value_);
+ }
+ };
Storage storage_;
};
}
template <class T>
-void swap(Optional<T>& a, Optional<T>& b) {
- if (a.hasValue() && b.hasValue()) {
- // both full
- using std::swap;
- swap(a.value(), b.value());
- } else if (a.hasValue() || b.hasValue()) {
- std::swap(a, b); // fall back to default implementation if they're mixed.
- }
+void swap(Optional<T>& a, Optional<T>& b) noexcept(noexcept(a.swap(b))) {
+ a.swap(b);
}
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>;
+};
+} // namespace experimental
+FOLLY_NAMESPACE_STD_END
+#endif // FOLLY_HAS_COROUTINES
projects / folly.git / blobdiff