callback compat (was: svn commit: r9664 ...)

On Mon, May 10, 2004 at 10:42:02AM -0400, Greg Hudson wrote:
>...
> What's the definition of "callback compatibility?" The implementation
> seems to simply reverse the direction of the compatibility test. To the
> best of my knowledge, we treat changing the signature of a callback as
> if it were changing the signature of any API which uses that callback,
> so we have no concept of "callback compatibility."

Correct.

The versioning guidelines are all about, "what happens when I update this
library? will my code continue to work? what do I need to do to make it
work post-upgrade?" So a callback signature cannot change, except across
major API upgrades of the library. Across minor upgrades, you can *add*
callbacks.

Consider that you have to get a callback *into* the library. Thus,
somewhere in the library's API is a signature holding the callback.
Changing the signature on the callback implies a signature change on the
function receiving the callback. Thus, you have the answer to how the
versioning applies here.

I hope that was clear enough.

Cheers,
-g

-- 
Greg Stein, http://www.lyra.org/
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