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+// Copyright 2010 The Kyua Authors.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors
+// may be used to endorse or promote products derived from this software
+// without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+/// \file utils/optional.hpp
+/// Provides the utils::optional class.
+///
+/// The class is provided as a separate module on its own to minimize
+/// header-inclusion side-effects.
+
+#if !defined(UTILS_OPTIONAL_HPP)
+#define UTILS_OPTIONAL_HPP
+
+#include "utils/optional_fwd.hpp"
+
+#include <ostream>
+
+namespace utils {
+
+
+/// Holds a data value or none.
+///
+/// This class allows users to represent values that may be uninitialized.
+/// Instead of having to keep separate variables to track whether a variable is
+/// supposed to have a value or not, this class allows multiplexing the
+/// behaviors.
+///
+/// This class is a simplified version of Boost.Optional.
+template< class T >
+class optional {
+ /// Internal representation of the optional data value.
+ T* _data;
+
+public:
+ optional(void);
+ optional(utils::detail::none_t);
+ optional(const optional< T >&);
+ explicit optional(const T&);
+ ~optional(void);
+
+ optional& operator=(utils::detail::none_t);
+ optional& operator=(const T&);
+ optional& operator=(const optional< T >&);
+
+ bool operator==(const optional< T >&) const;
+ bool operator!=(const optional< T >&) const;
+
+ operator bool(void) const;
+
+ const T& get(void) const;
+ const T& get_default(const T&) const;
+ T& get(void);
+};
+
+
+template< class T >
+std::ostream& operator<<(std::ostream&, const optional< T >&);
+
+
+template< class T >
+optional< T > make_optional(const T&);
+
+
+} // namespace utils
+
+#endif // !defined(UTILS_OPTIONAL_HPP)