UnitFactory.h

#ifndef MANTID_KERNEL_UNITFACTORYIMPL_H_
#define MANTID_KERNEL_UNITFACTORYIMPL_H_

/* Used to register unit classes into the factory. creates a global object in an
 * anonymous namespace. The object itself does nothing, but the comma operator
 * is used in the call to its constructor to effect a call to the factory's
 * subscribe method.
 *
 * The second operation that this macro performs is to provide the definition
 * of the unitID method for the concrete unit.
 */
#define DECLARE_UNIT(classname)                                                \
  namespace {                                                                  \
  Mantid::Kernel::RegistrationHelper                                           \
      register_alg_##classname(((Mantid::Kernel::UnitFactory::Instance()       \
                                     .subscribe<classname>(#classname)),       \
                                0));                                           \
  }                                                                            \
  const std::string Mantid::Kernel::Units::classname::unitID() const {         \
    return #classname;                                                         \
  }

//----------------------------------------------------------------------
// Includes
//----------------------------------------------------------------------
#include "MantidKernel/DllConfig.h"
#include "MantidKernel/DynamicFactory.h"
#include "MantidKernel/SingletonHolder.h"

namespace Mantid {
namespace Kernel {

//----------------------------------------------------------------------
// Forward declaration
//----------------------------------------------------------------------
class Unit;

/** Creates instances of concrete units.
    The factory is a singleton that hands out shared pointers to the base Unit
   class.
    It overrides the base class DynamicFactory::create method so that only a
   single
    instance of a given unit is ever created, and a pointer to that same
   instance
    is passed out each time the unit is requested.

    @author Russell Taylor, Tessella Support Services plc
    @date 13/03/2008

    Copyright &copy; 2008 ISIS Rutherford Appleton Laboratory, NScD Oak Ridge
   National Laboratory & European Spallation Source

    This file is part of Mantid.

    Mantid 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 3 of the License, or
    (at your option) any later version.

    Mantid 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, see <http://www.gnu.org/licenses/>.

    File change history is stored at: <https://github.com/mantidproject/mantid>
    Code Documentation is available at: <http://doxygen.mantidproject.org>
*/
class MANTID_KERNEL_DLL UnitFactoryImpl final : public DynamicFactory<Unit> {
public:
  UnitFactoryImpl(const UnitFactoryImpl &) = delete;
  UnitFactoryImpl &operator=(const UnitFactoryImpl &) = delete;

private:
  friend struct CreateUsingNew<UnitFactoryImpl>;

  /// Private Constructor for singleton class
  UnitFactoryImpl() = default;

  /// Private Destructor
  ~UnitFactoryImpl() override = default;
};

EXTERN_MANTID_KERNEL template class MANTID_KERNEL_DLL
    Mantid::Kernel::SingletonHolder<UnitFactoryImpl>;

using UnitFactory = SingletonHolder<UnitFactoryImpl>;

} // namespace Kernel
} // namespace Mantid

#endif /*MANTID_KERNEL_UNITFACTORYIMPL_H_*/