112 lines
3.4 KiB
C++
112 lines
3.4 KiB
C++
/*
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* Copyright (C) 2016 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <experimental/optional>
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#include <iostream>
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// optimized_optional<> is intended mainly for use with classes that store
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// their data externally and expect pointer to this data to be always non-null.
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// In such case there is no real need for another flag signifying whether
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// the optional is engaged.
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/*
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template<typename T>
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concept bool OptimizableOptional() {
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return stdx::is_default_constructible_v<T>
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&& stdx::is_nothrow_move_assignable_v<T>
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&& requires(const T& obj) {
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{ bool(obj) } noexcept;
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};
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}
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*/
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template<typename T>
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class optimized_optional {
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T _object;
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public:
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optimized_optional() = default;
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optimized_optional(std::experimental::nullopt_t) noexcept { }
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optimized_optional(const T& obj) : _object(obj) { }
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optimized_optional(T&& obj) noexcept : _object(std::move(obj)) { }
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optimized_optional(std::experimental::optional<T>&& obj) noexcept {
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if (obj) {
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_object = std::move(*obj);
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}
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}
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optimized_optional(const optimized_optional&) = default;
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optimized_optional(optimized_optional&&) = default;
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optimized_optional& operator=(std::experimental::nullopt_t) noexcept {
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_object = T();
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return *this;
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}
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template<typename U>
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std::enable_if_t<std::is_same<std::decay_t<U>, T>::value, optimized_optional&>
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operator=(U&& obj) noexcept {
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_object = std::forward<U>(obj);
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return *this;
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}
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optimized_optional& operator=(const optimized_optional&) = default;
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optimized_optional& operator=(optimized_optional&&) = default;
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explicit operator bool() const noexcept {
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return bool(_object);
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}
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T* operator->() noexcept { return &_object; }
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const T* operator->() const noexcept { return &_object; }
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T& operator*() noexcept { return _object; }
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const T& operator*() const noexcept { return _object; }
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bool operator==(const optimized_optional& other) const {
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return _object == other._object;
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}
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bool operator!=(const optimized_optional& other) const {
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return _object != other._object;
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}
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friend std::ostream& operator<<(std::ostream& out, const optimized_optional& opt) {
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if (!opt) {
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return out << "null";
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}
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return out << *opt;
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}
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};
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// In some cases move constructor may leave the moved object in a valid
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// disengaged state in which case there is no need to reconstruct the object
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// after move.
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template<typename T>
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struct move_constructor_disengages {
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enum { value = false };
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};
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template<typename T>
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inline optimized_optional<T> move_and_disengage(optimized_optional<T>& obj) {
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auto x = std::move(obj);
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if (!move_constructor_disengages<T>::value) {
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obj = { };
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}
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return x;
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}
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