Cross platform shit

inheritance.hpp

#pragma once

//
// Abstract interface
//
class IFile 
{
public:
  virtual ~IFile() = 0;

	virtual std::error_code read_async( std::int8_t*, std::size_t, std::function<void(std::error_code)> callback ) = 0;

	virtual std::error_code close( ) = 0;
};

//
// OS Implementation
//
class ConcreteFile : public IFile
{
	virtual std::error_code close( );
};

//
// Abstract Factory ( cross ) or Factor method 
//
class FileManager
{
	IFile* Open( const path&, ios::ios_base::openmode, std::error_code& )
	{
		return new ConcreteFile( ... );
	}
};

template.hpp

#pragma once

enum os
{
  windows,
	osx
};

template
<
	os osid
>
class File
{

	//
	// If you want them stack allocated :P
	//
	File( File&& );

	std::error_code close( );
};

template<>
class File<windows>
{
	File( File&& );

	std::error_code close( );
private:
	HANDLE m_hFile;
};

template<>
std::error_code File<windows>::close()
{
	//
	// Do something
	//
}

class FileManager
{
	File Open( const path&, iost::ios_base::openmode, std::error_code& )
	{
		#ifdef _WINDOWS
			return File<windows>( ... );
		#end
	}
} ;