singleton_base.h

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/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2019 John Wellbelove
Copyright(c) 2024 BMW AG
 
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#ifndef ETL_SINGLETON_BASE_INCLUDED
#define ETL_SINGLETON_BASE_INCLUDED

 
#include "platform.h"
#include "error_handler.h"
#include "file_error_numbers.h"
#include "nullptr.h"
 
namespace etl
{
  //*************************************************************************
  //*************************************************************************
  class singleton_base_exception : public etl::exception
  {
  public:
 
    singleton_base_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
      : exception(reason_, file_name_, line_number_)
    {
    }
  };
 
  //*************************************************************************
  //*************************************************************************
  class singleton_base_not_created : public etl::singleton_base_exception
  {
  public:
 
    singleton_base_not_created(string_type file_name_, numeric_type line_number_)
      : singleton_base_exception(ETL_ERROR_TEXT("singleton_base:not created", ETL_SINGLETON_BASE_FILE_ID"A"), file_name_, line_number_)
    {
    }
  };
 
  //*************************************************************************
  //*************************************************************************
  class singleton_base_already_created : public etl::singleton_base_exception
  {
  public:
 
    singleton_base_already_created(string_type file_name_, numeric_type line_number_)
      : singleton_base_exception(ETL_ERROR_TEXT("singleton_base:already created", ETL_SINGLETON_BASE_FILE_ID"B"), file_name_, line_number_)
    {
    }
  };
 
  //***********************************************************************
  //***********************************************************************
  template <typename T>
  class singleton_base
  {
  public:
 
    //***********************************************************************
    // Returns a reference to the instance.
    //***********************************************************************
    static T& instance()
    {
      ETL_ASSERT(m_self != ETL_NULLPTR, ETL_ERROR(etl::singleton_base_not_created));
 
      return *m_self;
    }
 
    //***********************************************************************
    //***********************************************************************
    static bool is_valid()
    {
      return (m_self != ETL_NULLPTR);
    }
 
  protected:
 
    //***********************************************************************
    //***********************************************************************
    explicit singleton_base(T& theInstance)
    {
      ETL_ASSERT(m_self == ETL_NULLPTR, ETL_ERROR(etl::singleton_base_already_created));
 
      m_self = &theInstance;
    }
 
    //***********************************************************************
    //***********************************************************************
    ~singleton_base()
    {
      m_self = ETL_NULLPTR;
    }
 
  private:
 
    static T* m_self;
  };
 
  //***********************************************************************
  //***********************************************************************
  template <class T>
  T* singleton_base<T>::m_self = ETL_NULLPTR;
} // namespace etl
 
#endif