/*
- * Copyright 2014 Facebook, Inc.
+ * 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.
* limitations under the License.
*/
-#ifndef FOLLY_OPTIONAL_H_
-#define FOLLY_OPTIONAL_H_
+#pragma once
/*
* Optional - For conditional initialization of values, like boost::optional,
* cout << *v << endl;
* }
*/
-#include <cassert>
+
#include <cstddef>
+#include <functional>
+#include <new>
+#include <stdexcept>
#include <type_traits>
#include <utility>
-#include <boost/operators.hpp>
-
+#include <folly/Launder.h>
#include <folly/Portability.h>
+#include <folly/Traits.h>
+#include <folly/Utility.h>
namespace folly {
-namespace detail { struct NoneHelper {}; }
+template <class Value>
+class Optional;
+
+namespace detail {
+struct NoneHelper {};
+
+// Allow each translation unit to control its own -fexceptions setting.
+// 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;
const None none = nullptr;
-/**
- * gcc-4.7 warns about use of uninitialized memory around the use of storage_
- * even though this is explicitly initialized at each point.
- */
-#if defined(__GNUC__) && !defined(__clang__)
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Wuninitialized"
-# pragma GCC diagnostic ignored "-Wpragmas"
-# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif // __GNUC__
-
-template<class Value>
+class OptionalEmptyException : public std::runtime_error {
+ public:
+ OptionalEmptyException()
+ : std::runtime_error("Empty Optional cannot be unwrapped") {}
+};
+
+template <class Value>
class Optional {
public:
- static_assert(!std::is_reference<Value>::value,
- "Optional may not be used with reference types");
+ typedef Value value_type;
- Optional()
- : hasValue_(false) {
- }
+ static_assert(
+ !std::is_reference<Value>::value,
+ "Optional may not be used with reference types");
+ static_assert(
+ !std::is_abstract<Value>::value,
+ "Optional may not be used with abstract types");
- Optional(const Optional& src)
- noexcept(std::is_nothrow_copy_constructible<Value>::value) {
+ FOLLY_CPP14_CONSTEXPR Optional() noexcept {}
+ Optional(const Optional& src) noexcept(
+ std::is_nothrow_copy_constructible<Value>::value) {
if (src.hasValue()) {
- construct(src.value());
- } else {
- hasValue_ = false;
+ storage_.construct(src.value());
}
}
- Optional(Optional&& src)
- noexcept(std::is_nothrow_move_constructible<Value>::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();
- } else {
- hasValue_ = false;
}
}
- /* implicit */ Optional(const None&) noexcept
- : hasValue_(false) {
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(const None&) noexcept {}
+
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(Value&& newValue) noexcept(
+ std::is_nothrow_move_constructible<Value>::value) {
+ storage_.construct(std::move(newValue));
}
- /* implicit */ Optional(Value&& newValue)
- noexcept(std::is_nothrow_move_constructible<Value>::value) {
- construct(std::move(newValue));
+ FOLLY_CPP14_CONSTEXPR /* implicit */ Optional(const Value& newValue) noexcept(
+ std::is_nothrow_copy_constructible<Value>::value) {
+ storage_.construct(newValue);
}
- /* implicit */ Optional(const Value& newValue)
- noexcept(std::is_nothrow_copy_constructible<Value>::value) {
- construct(newValue);
+ template <typename... Args>
+ FOLLY_CPP14_CONSTEXPR explicit Optional(in_place_t, Args&&... args) noexcept(
+ std::is_nothrow_constructible<Value, Args...>::value) {
+ storage_.construct(std::forward<Args>(args)...);
}
- ~Optional() noexcept {
- clear();
+ // 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()) {
- 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()) {
- value_ = newValue;
+ *storage_.value_pointer() = newValue;
} else {
- construct(newValue);
+ storage_.construct(newValue);
}
}
- template<class Arg>
+ template <class Arg>
Optional& operator=(Arg&& arg) {
assign(std::forward<Arg>(arg));
return *this;
}
- Optional& operator=(Optional &&other)
- noexcept (std::is_nothrow_move_assignable<Value>::value) {
-
+ Optional& operator=(Optional&& other) noexcept(
+ std::is_nothrow_move_assignable<Value>::value) {
assign(std::move(other));
return *this;
}
- Optional& operator=(const Optional &other)
- noexcept (std::is_nothrow_copy_assignable<Value>::value) {
-
+ Optional& operator=(const Optional& other) noexcept(
+ std::is_nothrow_copy_assignable<Value>::value) {
assign(other);
return *this;
}
- template<class... Args>
- void emplace(Args&&... args) {
+ template <class... Args>
+ Value& emplace(Args&&... args) {
clear();
- construct(std::forward<Args>(args)...);
+
return storage_.construct(std::forward<Args>(args)...);
}
- void clear() {
- if (hasValue()) {
- hasValue_ = false;
- value_.~Value();
+ 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();
+ return storage_.construct(ilist, std::forward<Args>(args)...);
+ }
+
+ void reset() noexcept {
+ storage_.clear();
+ }
+
+ 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();
}
}
- const Value& value() const {
- assert(hasValue());
- return value_;
+ FOLLY_CPP14_CONSTEXPR const Value& value() const & {
+ require_value();
+ return *storage_.value_pointer();
+ }
+
+ FOLLY_CPP14_CONSTEXPR Value& value() & {
+ require_value();
+ return *storage_.value_pointer();
}
- Value& value() {
- assert(hasValue());
- return value_;
+ FOLLY_CPP14_CONSTEXPR Value&& value() && {
+ require_value();
+ return std::move(*storage_.value_pointer());
}
- bool hasValue() const { return hasValue_; }
+ FOLLY_CPP14_CONSTEXPR const Value&& value() const && {
+ require_value();
+ return std::move(*storage_.value_pointer());
+ }
+
+ const Value* get_pointer() const & {
+ return storage_.value_pointer();
+ }
+ Value* get_pointer() & {
+ return storage_.value_pointer();
+ }
+ Value* get_pointer() && = delete;
- explicit operator bool() const {
- return hasValue();
+ FOLLY_CPP14_CONSTEXPR bool has_value() const noexcept {
+ return storage_.hasValue();
}
- const Value& operator*() const { return value(); }
- Value& operator*() { return value(); }
+ FOLLY_CPP14_CONSTEXPR bool hasValue() const noexcept {
+ return has_value();
+ }
- const Value* operator->() const { return &value(); }
- Value* operator->() { return &value(); }
+ FOLLY_CPP14_CONSTEXPR explicit operator bool() const noexcept {
+ return has_value();
+ }
+
+ FOLLY_CPP14_CONSTEXPR const Value& operator*() const & {
+ return value();
+ }
+ FOLLY_CPP14_CONSTEXPR Value& operator*() & {
+ return value();
+ }
+ FOLLY_CPP14_CONSTEXPR const Value&& operator*() const && {
+ return std::move(value());
+ }
+ FOLLY_CPP14_CONSTEXPR Value&& operator*() && {
+ return std::move(value());
+ }
+
+ FOLLY_CPP14_CONSTEXPR const Value* operator->() const {
+ return &value();
+ }
+ 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& {
- return hasValue_ ? value_ : std::forward<U>(dflt);
+ 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) && {
- return hasValue_ ? std::move(value_) : std::forward<U>(dflt);
+ FOLLY_CPP14_CONSTEXPR Value value_or(U&& dflt) && {
+ if (storage_.hasValue()) {
+ return std::move(*storage_.value_pointer());
+ }
+
+ return std::forward<U>(dflt);
}
private:
- template<class... Args>
- void construct(Args&&... args) {
- const void* ptr = &value_;
- // for supporting const types
- new(const_cast<void*>(ptr)) Value(std::forward<Args>(args)...);
- hasValue_ = true;
+ void require_value() const {
+ if (!storage_.hasValue()) {
+ detail::throw_optional_empty_exception();
+ }
}
- // uninitialized
- union { Value value_; };
- bool hasValue_;
-};
+ struct StorageTriviallyDestructible {
+ protected:
+ bool hasValue_;
+ typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+ value_[1];
+
+ public:
+ StorageTriviallyDestructible() : hasValue_{false} {}
+ void clear() {
+ hasValue_ = false;
+ }
+ };
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
+ struct StorageNonTriviallyDestructible {
+ protected:
+ bool hasValue_;
+ typename std::aligned_storage<sizeof(Value), alignof(Value)>::type
+ value_[1];
+
+ public:
+ StorageNonTriviallyDestructible() : hasValue_{false} {}
+ ~StorageNonTriviallyDestructible() {
+ clear();
+ }
+
+ void clear() {
+ if (hasValue_) {
+ hasValue_ = false;
+ launder(reinterpret_cast<Value*>(value_))->~Value();
+ }
+ }
+ };
+
+ struct Storage : std::conditional<
+ std::is_trivially_destructible<Value>::value,
+ StorageTriviallyDestructible,
+ StorageNonTriviallyDestructible>::type {
+ bool hasValue() const noexcept {
+ return this->hasValue_;
+ }
-template<class T>
+ 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>
const T* get_pointer(const Optional<T>& opt) {
- return opt ? &opt.value() : nullptr;
+ return opt.get_pointer();
}
-template<class T>
+template <class T>
T* get_pointer(Optional<T>& opt) {
- return opt ? &opt.value() : nullptr;
+ return opt.get_pointer();
}
-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.
- }
+template <class T>
+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) {
+template <class T, class Opt = Optional<typename std::decay<T>::type>>
+constexpr Opt make_optional(T&& v) {
return Opt(std::forward<T>(v));
}
///////////////////////////////////////////////////////////////////////////////
// Comparisons.
-template<class V>
-bool operator==(const Optional<V>& a, const V& b) {
+template <class U, class V>
+constexpr bool operator==(const Optional<U>& a, const V& b) {
return a.hasValue() && a.value() == b;
}
-template<class V>
-bool operator!=(const Optional<V>& a, const V& b) {
+template <class U, class V>
+constexpr bool operator!=(const Optional<U>& a, const V& b) {
return !(a == b);
}
-template<class V>
-bool operator==(const V& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator==(const U& a, const Optional<V>& b) {
return b.hasValue() && b.value() == a;
}
-template<class V>
-bool operator!=(const V& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator!=(const U& a, const Optional<V>& b) {
return !(a == b);
}
-template<class V>
-bool operator==(const Optional<V>& a, const Optional<V>& b) {
- if (a.hasValue() != b.hasValue()) { return false; }
- if (a.hasValue()) { return a.value() == b.value(); }
+template <class U, class V>
+FOLLY_CPP14_CONSTEXPR bool operator==(
+ const Optional<U>& a,
+ const Optional<V>& b) {
+ if (a.hasValue() != b.hasValue()) {
+ return false;
+ }
+ if (a.hasValue()) {
+ return a.value() == b.value();
+ }
return true;
}
-template<class V>
-bool operator!=(const Optional<V>& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator!=(const Optional<U>& a, const Optional<V>& b) {
return !(a == b);
}
-template<class V>
-bool operator< (const Optional<V>& a, const Optional<V>& b) {
- if (a.hasValue() != b.hasValue()) { return a.hasValue() < b.hasValue(); }
- if (a.hasValue()) { return a.value() < b.value(); }
+template <class U, class V>
+FOLLY_CPP14_CONSTEXPR bool operator<(
+ const Optional<U>& a,
+ const Optional<V>& b) {
+ if (a.hasValue() != b.hasValue()) {
+ return a.hasValue() < b.hasValue();
+ }
+ if (a.hasValue()) {
+ return a.value() < b.value();
+ }
return false;
}
-template<class V>
-bool operator> (const Optional<V>& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator>(const Optional<U>& a, const Optional<V>& b) {
return b < a;
}
-template<class V>
-bool operator<=(const Optional<V>& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator<=(const Optional<U>& a, const Optional<V>& b) {
return !(b < a);
}
-template<class V>
-bool operator>=(const Optional<V>& a, const Optional<V>& b) {
+template <class U, class V>
+constexpr bool operator>=(const Optional<U>& a, const Optional<V>& b) {
return !(a < b);
}
-// To supress comparability of Optional<T> with T, despite implicit conversion.
-template<class V> bool operator< (const Optional<V>&, const V& other) = delete;
-template<class V> bool operator<=(const Optional<V>&, const V& other) = delete;
-template<class V> bool operator>=(const Optional<V>&, const V& other) = delete;
-template<class V> bool operator> (const Optional<V>&, const V& other) = delete;
-template<class V> bool operator< (const V& other, const Optional<V>&) = delete;
-template<class V> bool operator<=(const V& other, const Optional<V>&) = delete;
-template<class V> bool operator>=(const V& other, const Optional<V>&) = delete;
-template<class V> bool operator> (const V& other, const Optional<V>&) = delete;
+// Suppress comparability of Optional<T> with T, despite implicit conversion.
+template <class V>
+bool operator<(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator<=(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator>=(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator>(const Optional<V>&, const V& other) = delete;
+template <class V>
+bool operator<(const V& other, const Optional<V>&) = delete;
+template <class V>
+bool operator<=(const V& other, const Optional<V>&) = delete;
+template <class V>
+bool operator>=(const V& other, const Optional<V>&) = delete;
+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
-#endif // FOLLY_OPTIONAL_H_
+// Allow usage of Optional<T> in std::unordered_map and std::unordered_set
+FOLLY_NAMESPACE_STD_BEGIN
+template <class T>
+struct hash<folly::Optional<T>> {
+ size_t operator()(folly::Optional<T> const& obj) const {
+ if (!obj.hasValue()) {
+ return 0;
+ }
+ return hash<typename remove_const<T>::type>()(*obj);
+ }
+};
+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
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