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diff --git a/src/utilities/functorPtr.hh b/src/utilities/functorPtr.hh
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+/*  This file is part of the OpenLB library
+ *
+ *  Copyright (C) 2017 Adrian Kummerlaender
+ *  E-mail contact: info@openlb.net
+ *  The most recent release of OpenLB can be downloaded at
+ *  <http://www.openlb.net/>
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License
+ *  as published by the Free Software Foundation; either version 2
+ *  of the License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public
+ *  License along with this program; if not, write to the Free
+ *  Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA  02110-1301, USA.
+*/
+
+#ifndef FUNCTOR_PTR_HH
+#define FUNCTOR_PTR_HH
+
+#include "functorPtr.h"
+
+#include "io/ostreamManager.h"
+
+namespace olb {
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr(F& f):
+  _ownF(),
+  _sharedF(),
+  _f(&f),
+  _owning(false)
+{ }
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr(F* f):
+  _ownF(),
+  _sharedF(),
+  _f(f),
+  _owning(false)
+{ }
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr(const std::unique_ptr<F>& f):
+  FunctorPtr(f.get())
+{ }
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr(std::unique_ptr<F>&& f):
+  _ownF(std::move(f)),
+  _f(_ownF.get()),
+  _owning(true)
+{ }
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr(std::shared_ptr<F> f):
+  _sharedF(std::move(f)),
+  _f(_sharedF.get()),
+  _owning(true)
+{ }
+
+template<typename F>
+FunctorPtr<F>::FunctorPtr():
+  FunctorPtr(nullptr)
+{ }
+
+template<typename F>
+typename std::add_lvalue_reference<F>::type FunctorPtr<F>::operator*() const
+{
+  return *_f;
+}
+
+template<typename F>
+typename std::add_pointer<F>::type FunctorPtr<F>::operator->() const noexcept
+{
+  return _f;
+}
+
+template<typename F>
+FunctorPtr<F>::operator bool() const
+{
+  return _f != nullptr;
+}
+
+template<typename F>
+bool FunctorPtr<F>::isOwning() const
+{
+  return _owning;
+}
+
+template<typename F>
+template<typename G>
+auto FunctorPtr<F>::toShared() -> typename std::enable_if< util::has_identity_functor<G>::value, std::shared_ptr<F>>::type
+{
+  if ( _owning && _ownF ) {
+    // convert unique_ptr to shared_ptr
+    _sharedF = std::shared_ptr<F>(std::move(_ownF));
+    _f       = _sharedF.get();
+    return _sharedF;
+  }
+  else if ( _sharedF ) {
+    // either we are owning or toShared was called previously and
+    // prepared a F::identity_functor_type we can reuse here:
+    return _sharedF;
+  }
+  else {
+#ifdef OLB_DEBUG_UNSAFE_FUNCTOR_ARITHMETIC
+    OstreamManager clerr(std::cerr,"FunctorPtr");
+    clerr << "WARNING: Non-owning functor wrapped in std::shared_ptr. Lifetime of composed functor is not guaranteed." << std::endl;
+#endif
+
+    // wrap non-owning pointer in identity functor
+    _sharedF = std::shared_ptr<F>(new typename F::identity_functor_type(*_f));
+    return _sharedF;
+  }
+}
+
+template<typename F>
+template<typename G>
+auto FunctorPtr<F>::toShared() -> typename std::enable_if<!util::has_identity_functor<G>::value, std::shared_ptr<F>>::type
+{
+  if ( _owning && _ownF ) {
+    // convert unique_ptr to shared_ptr
+    _sharedF = std::shared_ptr<F>(std::move(_ownF));
+    _f       = _sharedF.get();
+    return _sharedF;
+  }
+  else if ( _sharedF ) {
+    return _sharedF;
+  }
+  else {
+    OstreamManager clerr(std::cerr,"FunctorPtr");
+    clerr << "ERROR: No identity functor defined. Required to lift functor reference into std::shared_ptr arithmetic." << std::endl;
+    std::exit(-1);
+  }
+}
+
+}
+
+#endif