Optional.h

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/*
 * Copyright Onix Solutions Limited [OnixS]. All rights reserved.
 *
 * This software owned by Onix Solutions Limited [OnixS] and is protected by copyright law
 * and international copyright treaties.
 *
 * Access to and use of the software is governed by the terms of the applicable ONIXS Software
 * Services Agreement (the Agreement) and Customer end user license agreements granting
 * a non-assignable, non-transferable and non-exclusive license to use the software
 * for it's own data processing purposes under the terms defined in the Agreement.
 *
 * Except as otherwise granted within the terms of the Agreement, copying or reproduction of any part
 * of this source code or associated reference material to any other location for further reproduction
 * or redistribution, and any amendments to this copyright notice, are expressly prohibited.
 *
 * Any reproduction or redistribution for sale or hiring of the Software not in accordance with
 * the terms of the Agreement is a violation of copyright law.
 */

#pragma once

#include <OnixS/Senaf/MarketData/Export.h>

#include <new>

namespace OnixS { namespace Senaf { namespace MarketData {

template <typename T>
class Optional
{
public:
    /// Uninitialized instance.
    Optional() : init_(false) {}

    /// Constructs the optional object.
    Optional(const T& val) : init_(true)
    {
        construct(val);
    }

    /**
     * Initializes the contained value by copying the contained value of other,
     * but only if other is engaged. other is still in engaged state if it was
     * in engaged state before the call.
     */
    Optional(const Optional<T>& opt)
      : init_(opt.init_)
    {
        if (init_)
            construct(opt.get());
    }

    /// Assigns contents.
    Optional& operator=(const Optional<T>& opt)
    {
        destruct();

        if ((init_ = opt.init_))
            construct(opt.get());

        return *this;
    }

    /// Assigns contents.
    Optional& operator=(const T& val)
    {
        destruct();

        init_ = true;

        construct(val);

        return *this;
    }

    /// If engaged, destroys the contained value.
    ~Optional()
    {
        destruct();
    }

    /// Checks whether the object is in engaged state
    operator bool() const
    {
        return init_;
    }

    /// Returns a reference to the contained value.
    T& operator*()
    {
        return get();                                       // undefined if not initialized
    }

    /// Returns a const reference to the contained value.
    const T& operator*() const
    {
        return get();                                       // undefined if not initialized
    }

    /// A reference to the contained value.
    T& value()
    {
        return **this;
    }

    /// A const reference to the contained value.
    const T& value() const
    {
        return **this;
    }

    /// Reset stored value and set state to Uninitialized
    void reset()
    {
        destruct();

        init_ = false;
    }

protected:
    void* storage()
    {
        return data_;
    }

    const void* storage() const
    {
        return data_;
    }

    T& get()
    {
        return *static_cast<T*>(storage());
    }

    const T& get() const
    {
        return *static_cast<const T*>(storage());
    };

    void destruct()
    {
        if (init_) get().~T();
        init_ = false;
    }

    void construct(const T& data)
    {
        new (storage()) T(data);
    }

    char data_[sizeof(T)];
    bool init_;
};

}}}                                                        // namespace MarketData, Senaf, OnixS