- added Poco::Optional class template

Foundation/include/Poco/Optional.h

@@ -0,0 +1,183 @@
+//
+// Optional.h
+//
+// $Id: //poco/1.4/Foundation/include/Poco/Optional.h#1 $
+//
+// Library: Foundation
+// Package: Core
+// Module:  Optional
+//
+// Definition of the Optional class template.
+//
+// Copyright (c) 2012, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// Permission is hereby granted, free of charge, to any person or organization
+// obtaining a copy of the software and accompanying documentation covered by
+// this license (the "Software") to use, reproduce, display, distribute,
+// execute, and transmit the Software, and to prepare derivative works of the
+// Software, and to permit third-parties to whom the Software is furnished to
+// do so, all subject to the following:
+// 
+// The copyright notices in the Software and this entire statement, including
+// the above license grant, this restriction and the following disclaimer,
+// must be included in all copies of the Software, in whole or in part, and
+// all derivative works of the Software, unless such copies or derivative
+// works are solely in the form of machine-executable object code generated by
+// a source language processor.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+//
+
+
+#ifndef Foundation_Optional_INCLUDED
+#define Foundation_Optional_INCLUDED
+
+
+#include "Poco/Foundation.h"
+#include "Poco/Exception.h"
+#include <algorithm>
+
+
+namespace Poco {
+
+
+template <typename C>
+class Optional
+	/// Optional is a simple wrapper class for value types
+	/// that allows to introduce a specified/unspecified state
+	/// to value objects.
+	///
+	/// An Optional can be default constructed. In this case, 
+	/// the Optional will have a Null value and isSpecified() will
+	/// return false. Calling value()(without default value) on
+	/// a Null object will throw a NullValueException.
+	///
+	/// An Optional can also be constructed from a value.
+	/// It is possible to assign a value to an Optional, and
+	/// to reset an Optional to contain a Null value by calling
+	/// clear().
+	///
+	/// For use with Optional, the value type should support
+	/// default construction.
+	///
+	/// Note that the Optional class is basically the same as
+	/// Nullable. However, serializers may treat Nullable
+	/// and Optional differently. An example is XML serialization based
+	/// on XML Schema, where Optional would be used for an element with
+	/// minOccurs == 0, whereas Nullable would be used on an element with
+	/// nillable == true.
+{
+public:
+	Optional(): 
+		/// Creates an empty Optional.
+		_value(),
+		_isSpecified(false)
+	{
+	}
+
+	Optional(const C& value): 
+		/// Creates a Optional with the given value.
+		_value(value), 
+		_isSpecified(true)
+	{
+	}
+	
+	Optional(const Optional& other):
+		/// Creates a Optional by copying another one.
+		_value(other._value),
+		_isSpecified(other._isSpecified)
+	{
+	}
+
+	~Optional()
+		/// Destroys the Optional.
+	{
+	}
+
+	Optional& assign(const C& value)
+		/// Assigns a value to the Optional.
+	{
+		_value  = value;
+		_isSpecified = true;
+		return *this;
+	}
+	
+	Optional& assign(const Optional& other)
+		/// Assigns another Optional.
+	{
+		Optional tmp(other);
+		swap(tmp);
+		return *this;
+	}
+	
+	Optional& operator = (const C& value)
+	{
+		return assign(value);
+	}
+
+	Optional& operator = (const Optional& other)
+	{
+		return assign(other);
+	}
+
+	void swap(Optional& other)
+	{
+		std::swap(_value, other._value);
+		std::swap(_isSpecified, other._isSpecified);
+	}
+
+	const C& value() const
+		/// Returns the Optional's value.
+		///
+		/// Throws a Poco::NullValueException if the value has not been specified.
+	{
+		if (_isSpecified)
+			return _value;
+		else
+			throw Poco::NullValueException();
+	}
+
+	const C& value(const C& deflt) const
+		/// Returns the Optional's value, or the
+		/// given default value if the Optional's 
+		/// value has not been specified.
+	{
+		return _isSpecified ? _value : deflt;
+	}
+
+	bool isSpecified() const
+		/// Returns true iff the Optional's value has been specified.
+	{
+		return _isSpecified;
+	}
+	
+	void clear()
+		/// Clears the Optional.
+	{
+		_isSpecified = false;
+	}
+
+private:
+	C _value;
+	bool _isSpecified;
+};
+
+
+template <typename C>
+inline void swap(Optional<C>& n1, Optional<C>& n2)
+{
+	n1.swap(n2);
+}
+
+
+} // namespace Poco
+
+
+#endif // Foundation_Optional_INCLUDED