EncapsulatingSingleton.h

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/*
  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
*/

// EncapsulatingSingleton.h, (c) ATLAS Detector software
// Author: Thomas Gillam (thomas.gillam@cern.ch)
// ExpressionParsing library
 
#ifndef ENCAPSULATING_SINGLETON_H
#define ENCAPSULATING_SINGLETON_H
 
#include <stdexcept>
 
namespace ExpressionParsing {
  template <typename T> struct EncapsulatedDefault {
    typedef T type;
  };
 
  template <typename T> class EncapsulatingSingleton {
    public:
      static T *getInstance() {
        const EncapsulatingSingleton &instance = getSingleton();
        if (!instance.m_pointer) {
          throw std::runtime_error("EncapsulatingSingleton: Error - no instance loaded.");
        }
        return instance.m_pointer;
      }
 
      static void setInstance(T *proxyLoader) {
        EncapsulatingSingleton &instance = getSingleton();
        if (instance.m_pointer) {
          delete instance.m_pointer;
        }
        instance.m_pointer = proxyLoader;
      }
 
      static const EncapsulatingSingleton &getSingleton() {
        static const EncapsulatingSingleton instance;
        return instance;
      }
 
    private:
      EncapsulatingSingleton() { 
        typedef typename EncapsulatedDefault<T>::type Default;
        m_pointer = new Default();
      }
 
      ~EncapsulatingSingleton() {
        if (m_pointer) {
          delete m_pointer;
        }
      }
 
      EncapsulatingSingleton (const EncapsulatingSingleton&) = delete;
      EncapsulatingSingleton& operator= (const EncapsulatingSingleton&) = delete;
 
      T *m_pointer;
  };
}
 
#endif // ENCAPSULATING_SINGLETON_H