text: /*
  //@HEADER
  // *****************************************************************************
  //
  //                                  observer.h
  //                       DARMA/vt => Virtual Transport
  //
  // Copyright 2019-2021 National Technology & Engineering Solutions of Sandia, LLC
  // (NTESS). Under the terms of Contract DE-NA0003525 with NTESS, the U.S.
  // Government retains certain rights in this software.
  //
  // 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 the copyright holder 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.
  //
  // Questions? Contact darma@sandia.gov
  //
  // *****************************************************************************
  //@HEADER
  */
  
  #if !defined INCLUDED_VT_UTILS_PTR_OBSERVER_H
  #define INCLUDED_VT_UTILS_PTR_OBSERVER_H
  
  #include "vt/config.h"
  
  namespace vt { namespace util { namespace ptr {
  
  /**
   * \struct ObserverPtr
   *
   * \brief A simple wrapper over a raw pointer that indicates it is held as an
   * observer that does not own or control the lifetime.
   */
  template <typename T>
  struct ObserverPtr final {
  
    explicit ObserverPtr(T* in_p)
      : p_(in_p)
    { }
  
    ObserverPtr(std::nullptr_t) { }
    ObserverPtr() = default;
    ObserverPtr(ObserverPtr const&) = default;
    ObserverPtr(ObserverPtr&&) = default;
  
    ObserverPtr<T>& operator=(std::nullptr_t) {
      p_ = nullptr;
      return *this;
    }
  
    ObserverPtr<T>& operator=(T* in) {
      p_ = in;
      return *this;
    }
  
    ObserverPtr<T>& operator=(ObserverPtr<T> const& in) {
      p_ = in.p_;
      return *this;
    }
  
    bool operator==(T* n) const { return p_ == n; }
    bool operator!=(T* n) const { return p_ != n; }
    bool operator==(ObserverPtr<T> const& n) const { return p_ == n.p_; }
    bool operator!=(ObserverPtr<T> const& n) const { return p_ != n.p_; }
    bool operator==(std::nullptr_t) const { return p_ == nullptr; }
    bool operator!=(std::nullptr_t) const { return p_ != nullptr; }
  
    operator T*() const { return p_; }
    T* operator*() const { return p_; }
    T* operator->() const { return p_; }
    T* get() const { return p_; }
  
    void reset() { p_ = nullptr; }
  
  private:
    T* p_ = nullptr;
  };
  
  }}} /* end namespace vt::util::ptr */
  
  namespace vt { namespace util {
  
  template <typename T>
  using ObserverPtr = ptr::ObserverPtr<T>;
  
  }} /* end namespace vt::util */
  
  #endif /*INCLUDED_VT_UTILS_PTR_OBSERVER_H*/
  