An issue that came up discussing ASDF-FLV with Didier has to do with
outside modification to exported ASDF generic functions. I think it's
unambiguously reasonable to say "if you mess with unexported functions,
generic or otherwise, you're on your own, and could break things
arbitrarily."
But I don't think ASDF has established clear expectations about
extending methods of exported ASDF generic functions. I think there's
been an unspoken assumption that if ASDF generic functions are to be
extended, particularly by `:around`, `:before`, and `:after` methods,
there should be some novel class introduced that will be used to select
extensions. So, for example, it's fine to wrap or write new methods for
`perform`, but not for existing component and operation classes. Doing
so means that a change one might think appropriate for one's own library
bleeds out into other code that one has no way of predicting, and also
has the potential to collide with ASDF's own code or other people's ASDF
extensions.
Those are good reasons for this convention -- no modification without
introducing new classes for method dispatch -- but ASDF-FLV is an
example of a system that wants to introspect about the entire running
lisp image. I'd be interested in hearing what people think about this
kind of case. Should we introduce, for example, an `ASDF` object that
extenders could add mixins to in order to enable modifications to ASDF
behavior that aren't limited to a single library?
Please post any thoughts you have about this idea.
