ClickHouse/base/poco/Foundation/include/Poco/Optional.h

//
// Optional.h
//
// Library: Foundation
// Package: Core
// Module:  Optional
//
// Definition of the Optional class template.
//
// Copyright (c) 2012, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_Optional_INCLUDED
#define Foundation_Optional_INCLUDED


#include <algorithm>
#include "Poco/Exception.h"
#include "Poco/Foundation.h"


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