689 lines
18 KiB
C
689 lines
18 KiB
C
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/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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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/Portability.h>
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#include <folly/Traits.h>
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#include <folly/Utility.h>
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#include <folly/lang/Exception.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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explicit constexpr 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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constexpr 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.reset();
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}
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}
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constexpr /* implicit */ Optional(const None&) noexcept {}
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constexpr /* 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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constexpr /* 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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constexpr 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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constexpr 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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reset();
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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.reset();
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} else {
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reset();
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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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reset();
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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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reset();
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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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reset();
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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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constexpr 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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constexpr Value& value() & {
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require_value();
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return storage_.value;
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}
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constexpr 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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constexpr 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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constexpr bool has_value() const noexcept {
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return storage_.hasValue;
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}
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constexpr bool hasValue() const noexcept {
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return has_value();
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}
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constexpr explicit operator bool() const noexcept {
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return has_value();
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}
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constexpr const Value& operator*() const& {
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return value();
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}
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constexpr Value& operator*() & {
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return value();
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}
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constexpr const Value&& operator*() const&& {
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return std::move(value());
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}
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constexpr Value&& operator*() && {
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return std::move(value());
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}
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constexpr const Value* operator->() const {
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return &value();
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}
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constexpr 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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constexpr 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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constexpr 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 constexpr Optional<std::decay_t<T>> make_optional(T&&);
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template <class T, class... Args>
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friend constexpr Optional<T> make_optional(Args&&... args);
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template <class T, class U, class... As>
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friend constexpr 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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constexpr 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_exception<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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constexpr 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,
|
||
|
|
StorageTriviallyDestructible,
|
||
|
|
StorageNonTriviallyDestructible>::type;
|
||
|
|
|
||
|
|
Storage storage_;
|
||
|
|
};
|
||
|
|
|
||
|
|
template <class T>
|
||
|
|
const T* get_pointer(const Optional<T>& opt) {
|
||
|
|
return opt.get_pointer();
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class T>
|
||
|
|
T* get_pointer(Optional<T>& opt) {
|
||
|
|
return opt.get_pointer();
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class T>
|
||
|
|
void swap(Optional<T>& a, Optional<T>& b) noexcept(noexcept(a.swap(b))) {
|
||
|
|
a.swap(b);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class T>
|
||
|
|
constexpr Optional<std::decay_t<T>> make_optional(T&& v) {
|
||
|
|
using PrivateConstructor =
|
||
|
|
typename folly::Optional<std::decay_t<T>>::PrivateConstructor;
|
||
|
|
return {PrivateConstructor{}, std::forward<T>(v)};
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class T, class... Args>
|
||
|
|
constexpr folly::Optional<T> make_optional(Args&&... args) {
|
||
|
|
using PrivateConstructor = typename folly::Optional<T>::PrivateConstructor;
|
||
|
|
return {PrivateConstructor{}, std::forward<Args>(args)...};
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class T, class U, class... Args>
|
||
|
|
constexpr folly::Optional<T> make_optional(
|
||
|
|
std::initializer_list<U> il,
|
||
|
|
Args&&... args) {
|
||
|
|
using PrivateConstructor = typename folly::Optional<T>::PrivateConstructor;
|
||
|
|
return {PrivateConstructor{}, il, std::forward<Args>(args)...};
|
||
|
|
}
|
||
|
|
|
||
|
|
///////////////////////////////////////////////////////////////////////////////
|
||
|
|
// Comparisons.
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator==(const Optional<U>& a, const V& b) {
|
||
|
|
return a.hasValue() && a.value() == b;
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator!=(const Optional<U>& a, const V& b) {
|
||
|
|
return !(a == b);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator==(const U& a, const Optional<V>& b) {
|
||
|
|
return b.hasValue() && b.value() == a;
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator!=(const U& a, const Optional<V>& b) {
|
||
|
|
return !(a == b);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
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 U, class V>
|
||
|
|
constexpr bool operator!=(const Optional<U>& a, const Optional<V>& b) {
|
||
|
|
return !(a == b);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
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 U, class V>
|
||
|
|
constexpr bool operator>(const Optional<U>& a, const Optional<V>& b) {
|
||
|
|
return b < a;
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator<=(const Optional<U>& a, const Optional<V>& b) {
|
||
|
|
return !(b < a);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <class U, class V>
|
||
|
|
constexpr bool operator>=(const Optional<U>& a, const Optional<V>& b) {
|
||
|
|
return !(a < b);
|
||
|
|
}
|
||
|
|
|
||
|
|
// 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
|
||
|
|
|
||
|
|
// 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..
|
||
|
|
namespace std {
|
||
|
|
namespace experimental {
|
||
|
|
template <typename Value, typename... Args>
|
||
|
|
struct coroutine_traits<folly::Optional<Value>, Args...> {
|
||
|
|
using promise_type = folly::detail::OptionalPromise<Value>;
|
||
|
|
};
|
||
|
|
} // namespace experimental
|
||
|
|
} // namespace std
|
||
|
|
#endif // FOLLY_HAS_COROUTINES
|