106 lines
2.7 KiB
C++
106 lines
2.7 KiB
C++
/*
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Minetest
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Copyright (C) 2021 rubenwardy
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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This program 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 Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#pragma once
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#include <utility>
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#include "debug.h"
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struct nullopt_t
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{
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};
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constexpr nullopt_t nullopt{};
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/**
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* An implementation of optional for C++11, which aims to be
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* compatible with a subset of std::optional features.
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*
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* Unfortunately, Minetest doesn't use C++17 yet.
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*
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* @tparam T The type to be stored
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*/
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template <typename T>
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class Optional
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{
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bool m_has_value = false;
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T m_value;
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public:
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Optional() noexcept {}
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Optional(nullopt_t) noexcept {}
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Optional(const T &value) noexcept : m_has_value(true), m_value(value) {}
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Optional(T &&value) noexcept : m_has_value(true), m_value(std::move(value)) {}
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Optional(const Optional<T> &other) noexcept :
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m_has_value(other.m_has_value), m_value(other.m_value)
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{}
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Optional(Optional<T> &&other) noexcept :
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m_has_value(other.m_has_value), m_value(std::move(other.m_value))
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{
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other.m_has_value = false;
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}
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Optional<T> &operator=(nullopt_t) noexcept { m_has_value = false; return *this; }
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Optional<T> &operator=(const Optional<T> &other) noexcept
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{
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if (&other == this)
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return *this;
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m_has_value = other.m_has_value;
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m_value = other.m_value;
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return *this;
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}
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Optional<T> &operator=(Optional<T> &&other) noexcept
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{
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if (&other == this)
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return *this;
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m_has_value = other.m_has_value;
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m_value = std::move(other.m_value);
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other.m_has_value = false;
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return *this;
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}
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T &value()
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{
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FATAL_ERROR_IF(!m_has_value, "optional doesn't have value");
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return m_value;
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}
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const T &value() const
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{
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FATAL_ERROR_IF(!m_has_value, "optional doesn't have value");
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return m_value;
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}
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const T &value_or(const T &def) const { return m_has_value ? m_value : def; }
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// Unchecked access consistent with std::optional
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T* operator->() { return &m_value; }
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const T* operator->() const { return &m_value; }
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T& operator*() { return m_value; }
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const T& operator*() const { return m_value; }
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bool has_value() const noexcept { return m_has_value; }
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explicit operator bool() const { return m_has_value; }
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};
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