MIUtilSingletonBase.h

//===-- MIUtilSingletonBase.h -----------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#pragma once

namespace MI
{

//   MI::ISingleton base class usage:
//
//   class CMIDerivedClass
//       : public MI::ISingleton< CMIDerivedClass >
//   {
//       friend MI::ISingleton< CMIDerivedClass >;
//
//   // Overridden:
//   public:
//       // From MI::ISingleton
//       bool Initialize() override;
//       bool Shutdown() override;
//   };

//++ ============================================================================
// Details: Base class for the singleton pattern.
// Gotchas: Derived class must specify MI::ISingleton<> as a friend class.
//--
template <typename T> class ISingleton
{
    // Statics:
  public:
    // Return an instance of the derived class
    static T &
    Instance()
    {
        // This will fail if the derived class has not
        // declared itself to be a friend of MI::ISingleton
        static T instance;

        return instance;
    }

    // Overrideable:
  public:
    virtual bool Initialize() = 0;
    virtual bool Shutdown() = 0;
    //
    /* dtor */ virtual ~ISingleton(){}
};

} // namespace MI