1 files changed, 77 insertions, 0 deletions
diff --git a/src/util/Optional.h b/src/util/Optional.h
new file mode 100644
index 000000000..9c2842b43
--- /dev/null
+++ b/src/util/Optional.h
@@ -0,0 +1,77 @@
+/*
+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 "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(const Optional<T> &other) noexcept :
+			m_has_value(other.m_has_value), m_value(other.m_value)
+	{
+	}
+
+	void operator=(nullopt_t) noexcept { m_has_value = false; }
+
+	void operator=(const Optional<T> &other) noexcept
+	{
+		m_has_value = other.m_has_value;
+		m_value = other.m_value;
+	}
+
+	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; }
+
+	bool has_value() const noexcept { return m_has_value; }
+
+	explicit operator bool() const { return m_has_value; }
+};