fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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570 lines
14 KiB
570 lines
14 KiB
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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/*
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* Optional - For conditional initialization of values, like boost::optional,
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* but with support for move semantics and emplacement. Reference type support
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* has not been included due to limited use cases and potential confusion with
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* semantics of assignment: Assigning to an optional reference could quite
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* reasonably copy its value or redirect the reference.
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*
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* Optional can be useful when a variable might or might not be needed:
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*
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* Optional<Logger> maybeLogger = ...;
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* if (maybeLogger) {
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* maybeLogger->log("hello");
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* }
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*
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* Optional enables a 'null' value for types which do not otherwise have
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* nullability, especially useful for parameter passing:
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*
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* void testIterator(const unique_ptr<Iterator>& it,
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* initializer_list<int> idsExpected,
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* Optional<initializer_list<int>> ranksExpected = none) {
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* for (int i = 0; it->next(); ++i) {
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* EXPECT_EQ(it->doc().id(), idsExpected[i]);
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* if (ranksExpected) {
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* EXPECT_EQ(it->doc().rank(), (*ranksExpected)[i]);
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* }
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* }
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* }
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*
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* Optional models OptionalPointee, so calling 'get_pointer(opt)' will return a
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* pointer to nullptr if the 'opt' is empty, and a pointer to the value if it is
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* not:
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*
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* Optional<int> maybeInt = ...;
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* if (int* v = get_pointer(maybeInt)) {
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* cout << *v << endl;
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* }
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*/
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#include <cstddef>
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#include <functional>
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#include <new>
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#include <stdexcept>
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#include <type_traits>
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#include <utility>
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#include <folly/CPortability.h>
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#include <folly/Traits.h>
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#include <folly/Utility.h>
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namespace folly {
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template <class Value>
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class Optional;
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namespace detail {
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template <class Value>
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struct OptionalPromiseReturn;
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} // namespace detail
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struct None {
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enum class _secret { _token };
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/**
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* No default constructor to support both `op = {}` and `op = none`
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* as syntax for clearing an Optional, just like std::nullopt_t.
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*/
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constexpr explicit None(_secret) {}
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};
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constexpr None none{None::_secret::_token};
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class FOLLY_EXPORT OptionalEmptyException : public std::runtime_error {
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public:
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OptionalEmptyException()
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: std::runtime_error("Empty Optional cannot be unwrapped") {}
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};
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template <class Value>
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class Optional {
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public:
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typedef Value value_type;
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static_assert(
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!std::is_reference<Value>::value,
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"Optional may not be used with reference types");
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static_assert(
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!std::is_abstract<Value>::value,
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"Optional may not be used with abstract types");
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Optional() noexcept {}
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Optional(const Optional& src) noexcept(
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std::is_nothrow_copy_constructible<Value>::value) {
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if (src.hasValue()) {
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construct(src.value());
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}
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}
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Optional(Optional&& src) noexcept(
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std::is_nothrow_move_constructible<Value>::value) {
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if (src.hasValue()) {
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construct(std::move(src.value()));
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src.clear();
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}
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}
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/* implicit */ Optional(const None&) noexcept {}
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/* implicit */ Optional(Value&& newValue) noexcept(
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std::is_nothrow_move_constructible<Value>::value) {
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construct(std::move(newValue));
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}
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/* implicit */ Optional(const Value& newValue) noexcept(
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std::is_nothrow_copy_constructible<Value>::value) {
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construct(newValue);
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}
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template <typename... Args>
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explicit Optional(in_place_t, Args&&... args) noexcept(
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std::is_nothrow_constructible<Value, Args...>::value)
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: Optional{PrivateConstructor{}, std::forward<Args>(args)...} {}
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template <typename U, typename... Args>
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explicit Optional(
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in_place_t,
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std::initializer_list<U> il,
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Args&&... args) noexcept(std::
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is_nothrow_constructible<
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Value,
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std::initializer_list<U>,
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Args...>::value)
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: Optional{PrivateConstructor{}, il, std::forward<Args>(args)...} {}
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// Used only when an Optional is used with coroutines on MSVC
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/* implicit */ Optional(const detail::OptionalPromiseReturn<Value>& p)
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: Optional{} {
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p.promise_->value_ = this;
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}
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void assign(const None&) {
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clear();
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}
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void assign(Optional&& src) {
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if (this != &src) {
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if (src.hasValue()) {
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assign(std::move(src.value()));
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src.clear();
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} else {
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clear();
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}
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}
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}
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void assign(const Optional& src) {
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if (src.hasValue()) {
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assign(src.value());
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} else {
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clear();
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}
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}
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void assign(Value&& newValue) {
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if (hasValue()) {
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storage_.value = std::move(newValue);
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} else {
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construct(std::move(newValue));
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}
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}
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void assign(const Value& newValue) {
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if (hasValue()) {
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storage_.value = newValue;
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} else {
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construct(newValue);
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}
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}
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Optional& operator=(None) noexcept {
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reset();
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return *this;
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}
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template <class Arg>
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Optional& operator=(Arg&& arg) {
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assign(std::forward<Arg>(arg));
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return *this;
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}
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Optional& operator=(Optional&& other) noexcept(
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std::is_nothrow_move_assignable<Value>::value) {
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assign(std::move(other));
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return *this;
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}
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Optional& operator=(const Optional& other) noexcept(
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std::is_nothrow_copy_assignable<Value>::value) {
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assign(other);
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return *this;
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}
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template <class... Args>
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Value& emplace(Args&&... args) {
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clear();
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construct(std::forward<Args>(args)...);
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return value();
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}
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template <class U, class... Args>
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typename std::enable_if<
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std::is_constructible<Value, std::initializer_list<U>&, Args&&...>::value,
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Value&>::type
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emplace(std::initializer_list<U> ilist, Args&&... args) {
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clear();
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construct(ilist, std::forward<Args>(args)...);
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return value();
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}
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void reset() noexcept {
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storage_.clear();
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}
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void clear() noexcept {
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reset();
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}
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void swap(Optional& that) noexcept(IsNothrowSwappable<Value>::value) {
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if (hasValue() && that.hasValue()) {
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using std::swap;
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swap(value(), that.value());
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} else if (hasValue()) {
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that.emplace(std::move(value()));
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reset();
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} else if (that.hasValue()) {
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emplace(std::move(that.value()));
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that.reset();
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}
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}
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const Value& value() const& {
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require_value();
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return storage_.value;
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}
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Value& value() & {
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require_value();
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return storage_.value;
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}
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Value&& value() && {
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require_value();
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return std::move(storage_.value);
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}
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const Value&& value() const&& {
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require_value();
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return std::move(storage_.value);
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}
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const Value* get_pointer() const& {
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return storage_.hasValue ? &storage_.value : nullptr;
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}
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Value* get_pointer() & {
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return storage_.hasValue ? &storage_.value : nullptr;
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}
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Value* get_pointer() && = delete;
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bool has_value() const noexcept {
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return storage_.hasValue;
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}
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bool hasValue() const noexcept {
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return has_value();
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}
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explicit operator bool() const noexcept {
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return has_value();
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}
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const Value& operator*() const& {
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return value();
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}
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Value& operator*() & {
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return value();
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}
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const Value&& operator*() const&& {
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return std::move(value());
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}
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Value&& operator*() && {
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return std::move(value());
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}
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const Value* operator->() const {
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return &value();
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}
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Value* operator->() {
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return &value();
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}
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// Return a copy of the value if set, or a given default if not.
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template <class U>
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Value value_or(U&& dflt) const& {
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if (storage_.hasValue) {
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return storage_.value;
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}
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return std::forward<U>(dflt);
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}
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template <class U>
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Value value_or(U&& dflt) && {
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if (storage_.hasValue) {
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return std::move(storage_.value);
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}
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return std::forward<U>(dflt);
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}
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private:
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template <class T>
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friend Optional<_t<std::decay<T>>> make_optional(T&&);
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template <class T, class... Args>
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friend Optional<T> make_optional(Args&&... args);
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template <class T, class U, class... As>
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friend Optional<T> make_optional(std::initializer_list<U>, As&&...);
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/**
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* Construct the optional in place, this is duplicated as a non-explicit
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* constructor to allow returning values that are non-movable from
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* make_optional using list initialization.
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*
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* Until C++17, at which point this will become unnecessary because of
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* specified prvalue elision.
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*/
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struct PrivateConstructor {
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explicit PrivateConstructor() = default;
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};
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template <typename... Args>
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Optional(PrivateConstructor, Args&&... args) noexcept(
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std::is_constructible<Value, Args&&...>::value) {
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construct(std::forward<Args>(args)...);
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}
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void require_value() const {
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if (!storage_.hasValue) {
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throw OptionalEmptyException{};
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}
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}
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template <class... Args>
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void construct(Args&&... args) {
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const void* ptr = &storage_.value;
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// For supporting const types.
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new (const_cast<void*>(ptr)) Value(std::forward<Args>(args)...);
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storage_.hasValue = true;
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}
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struct StorageTriviallyDestructible {
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union {
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char emptyState;
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Value value;
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};
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bool hasValue;
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StorageTriviallyDestructible()
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: emptyState('\0'), hasValue{false} {}
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void clear() {
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hasValue = false;
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}
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};
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struct StorageNonTriviallyDestructible {
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union {
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char emptyState;
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Value value;
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};
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bool hasValue;
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StorageNonTriviallyDestructible() : hasValue{false} {}
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~StorageNonTriviallyDestructible() {
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clear();
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}
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void clear() {
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if (hasValue) {
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hasValue = false;
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value.~Value();
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}
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}
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};
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using Storage = typename std::conditional<
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std::is_trivially_destructible<Value>::value,
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StorageTriviallyDestructible,
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StorageNonTriviallyDestructible>::type;
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Storage storage_;
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};
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template <class T>
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const T* get_pointer(const Optional<T>& opt) {
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return opt.get_pointer();
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}
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template <class T>
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T* get_pointer(Optional<T>& opt) {
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return opt.get_pointer();
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}
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template <class T>
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void swap(Optional<T>& a, Optional<T>& b) noexcept(noexcept(a.swap(b))) {
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a.swap(b);
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}
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template <class T>
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Optional<_t<std::decay<T>>> make_optional(T&& v) {
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using PrivateConstructor =
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typename folly::Optional<_t<std::decay<T>>>::PrivateConstructor;
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return {PrivateConstructor{}, std::forward<T>(v)};
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}
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template <class T, class... Args>
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folly::Optional<T> make_optional(Args&&... args) {
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using PrivateConstructor = typename folly::Optional<T>::PrivateConstructor;
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return {PrivateConstructor{}, std::forward<Args>(args)...};
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}
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template <class T, class U, class... Args>
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folly::Optional<T> make_optional(
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std::initializer_list<U> il,
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Args&&... args) {
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using PrivateConstructor = typename folly::Optional<T>::PrivateConstructor;
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return {PrivateConstructor{}, il, std::forward<Args>(args)...};
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}
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///////////////////////////////////////////////////////////////////////////////
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// Comparisons.
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template <class U, class V>
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bool operator==(const Optional<U>& a, const V& b) {
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return a.hasValue() && a.value() == b;
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}
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template <class U, class V>
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bool operator!=(const Optional<U>& a, const V& b) {
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return !(a == b);
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}
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template <class U, class V>
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bool operator==(const U& a, const Optional<V>& b) {
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return b.hasValue() && b.value() == a;
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}
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template <class U, class V>
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bool operator!=(const U& a, const Optional<V>& b) {
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return !(a == b);
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}
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template <class U, class V>
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bool operator==(const Optional<U>& a, const Optional<V>& b) {
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if (a.hasValue() != b.hasValue()) {
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return false;
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}
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if (a.hasValue()) {
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return a.value() == b.value();
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}
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return true;
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}
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template <class U, class V>
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bool operator!=(const Optional<U>& a, const Optional<V>& b) {
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return !(a == b);
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}
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template <class U, class V>
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bool operator<(const Optional<U>& a, const Optional<V>& b) {
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if (a.hasValue() != b.hasValue()) {
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return a.hasValue() < b.hasValue();
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}
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if (a.hasValue()) {
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return a.value() < b.value();
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}
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return false;
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}
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template <class U, class V>
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bool operator>(const Optional<U>& a, const Optional<V>& b) {
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return b < a;
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}
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template <class U, class V>
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bool operator<=(const Optional<U>& a, const Optional<V>& b) {
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return !(b < a);
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}
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template <class U, class V>
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bool operator>=(const Optional<U>& a, const Optional<V>& b) {
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return !(a < b);
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}
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// Suppress comparability of Optional<T> with T, despite implicit conversion.
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template <class V>
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bool operator<(const Optional<V>&, const V& other) = delete;
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template <class V>
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bool operator<=(const Optional<V>&, const V& other) = delete;
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template <class V>
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bool operator>=(const Optional<V>&, const V& other) = delete;
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template <class V>
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bool operator>(const Optional<V>&, const V& other) = delete;
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template <class V>
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bool operator<(const V& other, const Optional<V>&) = delete;
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template <class V>
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bool operator<=(const V& other, const Optional<V>&) = delete;
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template <class V>
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bool operator>=(const V& other, const Optional<V>&) = delete;
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template <class V>
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bool operator>(const V& other, const Optional<V>&) = delete;
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// Comparisons with none
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template <class V>
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bool operator==(const Optional<V>& a, None) noexcept {
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return !a.hasValue();
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}
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template <class V>
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bool operator==(None, const Optional<V>& a) noexcept {
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return !a.hasValue();
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}
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template <class V>
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bool operator<(const Optional<V>&, None) noexcept {
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return false;
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}
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template <class V>
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bool operator<(None, const Optional<V>& a) noexcept {
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return a.hasValue();
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}
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template <class V>
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bool operator>(const Optional<V>& a, None) noexcept {
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return a.hasValue();
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}
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template <class V>
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bool operator>(None, const Optional<V>&) noexcept {
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return false;
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}
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template <class V>
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bool operator<=(None, const Optional<V>&) noexcept {
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return true;
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}
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template <class V>
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bool operator<=(const Optional<V>& a, None) noexcept {
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return !a.hasValue();
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}
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template <class V>
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bool operator>=(const Optional<V>&, None) noexcept {
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return true;
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}
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template <class V>
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bool operator>=(None, const Optional<V>& a) noexcept {
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return !a.hasValue();
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}
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///////////////////////////////////////////////////////////////////////////////
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} // namespace folly
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