[gmpi] Re: low level API
- From: Tim Hockin <thockin@xxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Thu, 3 Feb 2005 23:26:12 -0800
On Wed, Feb 02, 2005 at 01:14:40PM +0000, Angus F. Hewlett wrote:
> >The advantage of a dispatcher is you can extend the API by
> >adding new opcodes, you don't change the binary interface,
> >makes backward/forward compatibilty very easy.
> >
> >
> That's very true. However, it depends on the richness, modularity and
> object-ness of the API.
>
> For instance, if a GMPI Event is expected in some ways to behave like an
> object (with get/set methods mediated via the dispatcher), when you
> extend the functionality you can end up with a highly
> disordered/unsorted list of dispatcher opcodes.. either that or you have
> to reserve plenty of space in the opcode enumeration so as to keep like
> with like - so that all messages beginning with 0x1000 relate to
> initialisation, 0x2000 to pins and connection, 0x3000 to events...
The worst part about a dispatcher is that the opcodes become scoped much
wider than they need to be, and the data gets farther from the meaning.
If I want to address a "method" of the third foo in the bar array of
object o, you end up with something like
o->dispatch(o, OBJ_BAR_METHOD, 3, args...);
which is a lot nastier than
o->bar[3]->method(args)
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