[gmpi] Re: low level API - Abstract Factory summary
- From: jeffmcc@xxxxxxxxxx
- To: gmpi@xxxxxxxxxxxxx
- Date: Wed, 09 Feb 2005 14:06:28 +1300
Rumour has it, when one finally 'gets' COM ...you hear
angels sing and the sun seems brighter.
I think I'm getting closer. Summary:
dll has one entry point only, the factory.
First you ask the factory for the 'metadata library'
interface..
2nd, you use the library to iterate the list of plugins.
The library gives you each plugin's Unique ID, name and
other metadata about it.
3rd, you pass a plugin's unique ID to the factory, it passes
back a GMPI_Plugin (interface).
Quite involved, but also quite future-proof.
Jeff
>
> Perhaps a more COM-like way to do this, is everything that
> comes out of a factory is an interface.
>
> /**
> * Factory in a plugin library for plugins.
> */
> class GMPI_IPluginLibrary : public GMPI_IUnknown
> {
> GMPI_Result GMPI_EnumeratePlugins(GMPI_PluginDescriptor
> *descriptor, int32_t index);
> };
>
> Original Message:
> -----------------
> From: jeffmcc@xxxxxxxxxx
> Date: Wed, 09 Feb 2005 12:33:33 +1300
> To: gmpi@xxxxxxxxxxxxx
> Subject: [gmpi] Re: low level API - Abstract Factory
> summary
>
>
> > HRESULT CreateFactory( CLSID clsidClass, IFactory**
> ppFactory );
>
> Hi Ron,
> So each plugin has a unique ID code, we pass that to the
> factory, it returns a GMPI_Plugin interface. That's
> good...
>
> But we first need the list of available IDs (in that dll).
> So don't we need a second function too, that given an
> index, returns the metadata for a plugin in the dll?
>
> HRESULT GetGMPI_PluginDescriptor( int index,
> IGMPI_PluginDescriptor **pd );
>
> The metadata interface supplys the plugin's unique ID,
> it's name etc.
>
> Am I on the right track?
>
> Jeff
>
> PS: mayby replace HRESULT with GMPI_RESULT.
>
> >
> > >>>
> > I think making it an object is just OO masturbation. It
> > feels good, but it doesn't really achieve anything.
> > <<<
> >
> > The reason it seems overengineered is because the factor
> > interface hasn't been defined properly. I reall should
> > be something like this:
> >
> > struct IFactory
> > {
> > HRESULT CreateInstance( IUnknown** ppObj ) = 0;
> > };
> >
> > HRESULT CreateFactory( CLSID clsidClass, IFactory**
> > ppFactory );
> >
> > The idea is: a single module can be a factory for a
> > variety of different classes. You instantiate new
> > objects of a class through the factory for the class,
> > and you get the identify the factory by CLSID (GUID).
> >
> >
> >
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