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/*
Minetest
Copyright (C) 2021 rubenwardy
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#pragma once
#include <utility>
#include "debug.h"
struct nullopt_t
{
};
constexpr nullopt_t nullopt{};
/**
* An implementation of optional for C++11, which aims to be
* compatible with a subset of std::optional features.
*
* Unfortunately, Minetest doesn't use C++17 yet.
*
* @tparam T The type to be stored
*/
template <typename T>
class Optional
{
bool m_has_value = false;
T m_value;
public:
Optional() noexcept {}
Optional(nullopt_t) noexcept {}
Optional(const T &value) noexcept : m_has_value(true), m_value(value) {}
Optional(T &&value) noexcept : m_has_value(true), m_value(std::move(value)) {}
Optional(const Optional<T> &other) noexcept :
m_has_value(other.m_has_value), m_value(other.m_value)
{}
Optional(Optional<T> &&other) noexcept :
m_has_value(other.m_has_value), m_value(std::move(other.m_value))
{
other.m_has_value = false;
}
Optional<T> &operator=(nullopt_t) noexcept { m_has_value = false; return *this; }
Optional<T> &operator=(const Optional<T> &other) noexcept
{
if (&other == this)
return *this;
m_has_value = other.m_has_value;
m_value = other.m_value;
return *this;
}
Optional<T> &operator=(Optional<T> &&other) noexcept
{
if (&other == this)
return *this;
m_has_value = other.m_has_value;
m_value = std::move(other.m_value);
other.m_has_value = false;
return *this;
}
T &value()
{
FATAL_ERROR_IF(!m_has_value, "optional doesn't have value");
return m_value;
}
const T &value() const
{
FATAL_ERROR_IF(!m_has_value, "optional doesn't have value");
return m_value;
}
const T &value_or(const T &def) const { return m_has_value ? m_value : def; }
// Unchecked access consistent with std::optional
T* operator->() { return &m_value; }
const T* operator->() const { return &m_value; }
T& operator*() { return m_value; }
const T& operator*() const { return m_value; }
bool has_value() const noexcept { return m_has_value; }
explicit operator bool() const { return m_has_value; }
};
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