factory.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library 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
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA



#ifndef LIBMESH_FACTORY_H
#define LIBMESH_FACTORY_H


// Local includes
#include "libmesh/libmesh_common.h"

// C++ includes
#include <cstddef>
#include <map>
#include <memory> // make_unique
#include <string>

namespace libMesh
{



template <class Base>
class Factory
{
protected:

  Factory (const std::string & name);

public:

  virtual ~Factory () = default;

  static std::unique_ptr<Base> build (const std::string & name);

  virtual std::unique_ptr<Base> create () = 0;


protected:

  static std::map<std::string, Factory<Base> *> & factory_map();
};



template <class Derived, class Base>
class FactoryImp: public Factory<Base>
{
public:

  FactoryImp (const std::string & name) : Factory<Base>(name) { }

  ~FactoryImp () = default;

private:

  virtual std::unique_ptr<Base> create () override;
};



// -----------------------------------------------------
// Factory members
template <class Base>
inline
Factory<Base>::Factory (const std::string & name)
{
  // Make sure we haven't already added this name
  // to the map
  libmesh_assert (!factory_map().count(name));

  factory_map()[name] = this;
}



template <class Base>
inline
std::unique_ptr<Base> Factory<Base>::build (const std::string & name)
{
  // name not found in the map
  if (!factory_map().count(name))
    {
      libMesh::err << "Tried to build an unknown type: " << name << std::endl;

      libMesh::err << "valid options are:" << std::endl;

      for (const auto & pr : factory_map())
        libMesh::err << "  " << pr.first << std::endl;

      libmesh_error_msg("Exiting...");
    }

  Factory<Base> * f = factory_map()[name];
  return std::unique_ptr<Base>(f->create());
}



template <class Derived, class Base>
inline
std::unique_ptr<Base> FactoryImp<Derived,Base>::create ()
{
  return std::make_unique<Derived>();
}


} // namespace libMesh

#endif // LIBMESH_FACTORY_H