[Python-3000] Another generic functions/adaptation use case

[Guido van Rossum]

On 4/14/06, Nick Coghlan <ncoghlan at iinet.net.au> wrote:
> Another potential generic function use case that occurred to me is the open()
> builtin.
>
> If that was extensible, the discussion about providing a nice filesystem path
> abstraction in the standard lib wouldn't need to waste any time on the
> question of whether or not to inherit from unicode - it would just register a
> new open() signature for path objects.

It  needn't waste time on that question anyway -- the only sensible
answer is no.

> Ditto for if we later added objects to represent URLs/URIs.

I'm not sure I follow this whole use case. Different VFSs probably all
represent their pathnames as strings (at some level) so the type
wouldn't be a useful differentiator. If you already have a path object
specific to a VFS (or one for the URL space), the open operation
should just be a method on the path object. Generic/overloaded
functions (of the kind dispatched on the argument type(s)) mainly have
a place when the operation is defined separate from the object. That's
not a reasonable assumption in your use case -- the path object is
defined in close coordination with the open() implementation so
there's no decoupling requirement; a regular method is fine.

--
--Guido van Rossum (home page: http://www.python.org/~guido/)