propagate_const.h

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#ifndef FWCore_Utilities_propagate_const_h
#define FWCore_Utilities_propagate_const_h
// -*- C++ -*-
//
// Package:     FWCore/Utilities
// Class  :     propagate_const
// 
//
// Original Author:  Chris Jones
//         Created:  Fri, 18 Dec 2015 14:56:12 GMT
//

// system include files
#include <type_traits>
#include <utility>

// user include files

// forward declarations

namespace edm {

  template<typename T>
  class propagate_const;

  template<typename T> T& get_underlying( propagate_const<T>& );
  template<typename T> T const& get_underlying( propagate_const<T> const& );
  
  
  template<typename T>
  class propagate_const
  {
    
  public:
    friend T& get_underlying<T>( propagate_const<T>& );
    friend T const& get_underlying<T>( propagate_const<T> const& );
    
    using element_type = typename std::remove_reference<decltype(*std::declval<T&>())>::type;
    
    propagate_const() = default;
    
    propagate_const( propagate_const<T>&&) = default;
    propagate_const( propagate_const<T> const&) = delete;
    template<typename U>
    propagate_const( U&& iValue) : m_value(std::forward<U>(iValue)) {}

    
    propagate_const<T>& operator=(propagate_const&&) = default;
    propagate_const<T>& operator=(propagate_const<T> const&) = delete;
    
    template<typename U>
    propagate_const& operator=(U&& iValue) {
      m_value = std::forward<U>(iValue);
      return *this;
    }
    
    
    
    // ---------- const member functions ---------------------
    element_type const* get() const { return &(*m_value); }
    element_type const* operator->() const { return this->get(); }
    element_type const& operator*() const { return *m_value; }
    
    operator element_type const* () const { return this->get(); }
    
    // ---------- member functions ---------------------------
    element_type* get() { return &(*m_value); }
    element_type* operator->() { return this->get(); }
    element_type& operator*() { return *m_value; }

    operator element_type* () { return this->get(); }
    
  private:
    
    // ---------- member data --------------------------------
    T m_value;
  };
  
  template<typename T> T& get_underlying( propagate_const<T>& iP) { return iP.m_value;}
  template<typename T> T const& get_underlying( propagate_const<T> const& iP ) {return iP.m_value;}

}


#endif