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framework/common/optional.h

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+/* Copyright (c) 2021, Arm Limited and Contributors
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cassert>
+
+namespace vkb
+{
+// Simple optional class for pre c++17 std::optional
+// May be replaced by std::optional in the future
+template <typename Type>
+class Optional
+{
+  public:
+	virtual ~Optional() = default;
+	Optional()          = default;
+
+	Optional(const Optional &optional);
+
+	template <typename U = Type>
+	Optional(const U &value);
+
+	bool        has_value() const;
+	const Type &value() const;
+	const Type  value_or(Type &&alternative) const;
+	const Type  value_or(const Type &alternative = {}) const;
+
+	Optional &operator=(Optional &&opt)
+	{
+		_has_value = opt._has_value;
+		_value     = opt._value;
+		return *this;
+	}
+
+	template <typename U = Type>
+	Optional &operator=(U &&value)
+	{
+		_has_value = true;
+		_value     = value;
+		return *this;
+	}
+
+	Optional &operator=(const Optional &value)
+	{
+		_has_value = value._has_value;
+		_value     = value._value;
+		return *this;
+	}
+
+	template <typename U = Type>
+	Optional &operator=(U *value)
+	{
+		if (value == nullptr)
+		{
+			_has_value = false;
+			return *this;
+		}
+
+		_has_value = true;
+		_value     = *value;
+		return *this;
+	}
+
+  private:
+	bool _has_value = false;
+	Type _value;
+};
+
+template <typename Type>
+Optional<Type>::Optional(const Optional &optional)
+{
+	_has_value = optional._has_value;
+	_value     = optional._value;
+}
+
+template <typename Type>
+template <typename U>
+Optional<Type>::Optional(const U &value)
+{
+	_has_value = true;
+	_value     = value;
+}
+
+template <typename Type>
+bool Optional<Type>::has_value() const
+{
+	return _has_value;
+}
+
+template <typename Type>
+const Type &Optional<Type>::value() const
+{
+	assert(_has_value && "Value does not exist");
+	return _value;
+}
+
+template <typename Type>
+const Type Optional<Type>::value_or(Type &&alternative) const
+{
+	if (has_value())
+	{
+		return _value;
+	}
+
+	return alternative;
+}
+
+template <typename Type>
+const Type Optional<Type>::value_or(const Type &alternative) const
+{
+	if (has_value())
+	{
+		return _value;
+	}
+
+	return alternative;
+}
+}        // namespace vkb