boost::intrusive_ptr support for COM objects, based on https://github.com/rengeln/nyx/blob/master/src/Prefix.h (see also http://code-freeze.blogspot.com/2012/02/using-intrusiveptr-with-com.html)

intrusive_ptr_COM.h

/** @file
    @brief Header providing for usage of boost::intrusive_ptr with COM.

    Based on the header found at:
    <https://github.com/rengeln/nyx/blob/master/src/Prefix.h>

    It is essentially the code from the author's blog post,
    <http://code-freeze.blogspot.com/2012/02/using-intrusiveptr-with-com.html>
    , which describes usage and motivation more. However, it appears to have
    some small improvements (mainly in style, and C++11 usage), and usefully,
    it has a standard license associated with it.

    @date 2011

    @author
    Robert Engeln <engeln@gmail.com>
*/

// Excerpted from <https://github.com/rengeln/nyx/blob/master/src/Prefix.h>
//
// Original header, then accompanying LICENSE file (which matches the MIT
// license as found at http://opensource.org/licenses/mit-license) are
// reproduced below.

///////////////////////////////////////////////////////////////////////////////
//	Copyright (C) 2011 Robert Engeln (engeln@gmail.com) All rights reserved.
//	See accompanying LICENSE file for full license information.
///////////////////////////////////////////////////////////////////////////////

/* Original LICENSE file, line wrapped at 72

Copyright (C) 2012 Robert Engeln (engeln@gmail.com)

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

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 AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

*/


#ifndef INCLUDED_intrusive_ptr_COM_h_GUID_BB97FC94_B320_4FB9_5379_940B0A631CA6
#define INCLUDED_intrusive_ptr_COM_h_GUID_BB97FC94_B320_4FB9_5379_940B0A631CA6

#ifndef COM_NO_WINDOWS_H
#define COM_NO_WINDOWS_H
#endif
#include <unknwn.h>
#include <boost/intrusive_ptr.hpp>


//
//  Enable intrusive_ptr to work with COM objects.
//
inline void intrusive_ptr_add_ref(IUnknown* ptr)
{
    ptr->AddRef();
}

inline void intrusive_ptr_release(IUnknown* ptr)
{
    ptr->Release();
}

//
//  Enable intrusive_ptr objects to be passed as parameters to functions expecting
//  a pointer-to-pointer which will be initialized by the function.
//
template <typename T>
class IntrusivePtrWrapper
{
public:
    //
    //  Constructor.
    //
    //  Parameters:
    //      [in] ref
    //          Intrusive_ptr object to wrap.
    //      [in] addRef
    //          If true then the ptr's refcount will be incremented on acquisition.
    //
    IntrusivePtrWrapper(boost::intrusive_ptr<T>& ref, bool addRef);

    //
    //  Destructor.
    //
    ~IntrusivePtrWrapper();

    //
    //  Implicit conversion to T**.
    //
    operator T**();

    //
    //  Implicit conversion to void**.
    //
    operator void**();

private:
    //
    //  Properties.
    //
    boost::intrusive_ptr<T>& m_ref;
    T* m_ptr;
    bool m_addRef;
};

template <typename T>
inline IntrusivePtrWrapper<T>::IntrusivePtrWrapper(boost::intrusive_ptr<T>& ref, bool addRef)
    : m_ref(ref), m_addRef(addRef), m_ptr(nullptr)
{
}

template <typename T>
inline IntrusivePtrWrapper<T>::~IntrusivePtrWrapper()
{
    m_ref = boost::intrusive_ptr<T>(m_ptr, m_addRef);
}

template <typename T>
inline IntrusivePtrWrapper<T>::operator T**()
{
    return &m_ptr;
}

template <typename T>
inline IntrusivePtrWrapper<T>::operator void**()
{
    return reinterpret_cast<void**>(&m_ptr);
}

//
//  Helper function for constructing an IntrusivePtrWrapper.
//
//  Parameters:
//      [in] ref
//          Intrusive_ptr object to wrap.
//      [in] addRef
//          If true then the ptr's refcount will be incremented on acquisition.
//          Default is false, which matches the behavior of COM functions.
//
template <typename T>
inline IntrusivePtrWrapper<T> AttachPtr(boost::intrusive_ptr<T>& ref, bool addRef = false)
{
    return IntrusivePtrWrapper<T>(ref, addRef);
}

#endif // INCLUDED_intrusive_ptr_COM_h_GUID_BB97FC94_B320_4FB9_5379_940B0A631CA6

Since integrated and updated here: https://github.com/OSVR/OSVR-Core/blob/master/vendor/com_smart_pointer/intrusive_ptr_COM.h