Re: Plugin architecture design

[Gregory Martin Pfeil]

On Tuesday, April 30, 2002, at 07:49  AM, e.sammer wrote:

> Stephen Brandon wrote:
> > Versioning
> > ------------
> > I have also thought about the need for versioning the API - if the API 
> > evolves we don't want to break old plugins. So perhaps we publish an 
> > API in the MK with textual/numeric tags, which the plugin can return 
> > in a dictionary when loaded, corresponding to which APIs it supports.
>
> I would think that the best way to support versioning of the protocol 
> or plugin api would be to have a protocol method the plugin would have 
> to implement that returns the version of the api like:
>
> @protocol MusicKitPlugin
> + (NSString*)protocolVersion;
> @end
>
> This way, the plugin could do things like forwardInvocation if it wants 
> to dynamically "alter" it's protocol version. Another idea might be to 
> query the delegate for which protocol version it wants and go from 
> there.

I've always felt that the best way to support versioning is a method 
like:

+ (bool) supportsVersion: (NSString) version;

That way, an implementation can support multiple versions of the 
protocol, and a sort of negotiation can go on. The application can check 
against its preferred version, then fall back on other versions (after 
checking to see if they're supported) if the preferred one isn't.