On Wed, Jun 24, 2020 at 3:49 PM Ethan Furman <et...@stoneleaf.us> wrote:
>
> On 06/23/2020 10:31 PM, Chris Angelico wrote:
> > On Wed, Jun 24, 2020 at 3:21 PM Ethan Furman wrote:
> >> On 06/23/2020 09:01 AM, PEP 622 wrote:
> >>
> >>> from enum import Enum
> >>>
> >>> class Color(Enum):
> >>> BLACK = 1
> >>> RED = 2
> >>>
> >>> BLACK = 1
> >>> RED = 2
> >>>
> >>> match color:
> >>> case .BLACK | Color.BLACK:
> >>> print("Black suits every color")
> >>> case BLACK: # This will just assign a new value to BLACK.
> >>> ...
> >>
> >> As others have noted, the leading dot to disambiguate between a name
> >> assignment and a value check is going to be a problem. I think it's also
> >> unnecessary because instead of
> >>
> >> case BLACK:
> >> blahblah()
> >>
> >> we can do
> >>
> >> case _:
> >> # look ma! BLACK is just "color"!
> >> BLACK = color # if you really want it bound to another name
> >>
> >> In other words, the PEP is currently building in two ways to do the same
> >> thing -- make a default case. One of those ways is going to be a pain;
> >> the other, once renamed to "else", will be perfect! :-) As a bonus, no
> >> special casing for leading dots.
> >>
> >
> > But what if that's composed into something else?
> >
> > class Room(Enum):
> > LIBRARY = 1
> > BILLIARD_ROOM = 2
> > ...
> >
> > match accusation:
> > case (Color.SCARLETT, Room.BILLIARD_ROOM):
> > print("Correct")
> > case (Color.SCARLETT, _):
> > print("Not there!")
> > case (_, Room.BILLIARD_ROOM):
> > print("Wrong person!")
> > case (_, _):
> > print("Nope. Just nope.")
> >
> > Without the dots, there's no way to tell whether you're matching
> > specific values in the tuple, or matching by length alone and then
> > capturing. You can't use the 'else' keyword for a partial match.
>
> Well, your example isn't using leading dots like `.BLACK` is, and your
> example isn't using `case _` as a final catch-all, and your example isn't
> using "case some_name_here" as an always True match. In other words, your
> example isn't talking about what I'm talking about. ;-)
>
But it IS using "_" as a catch-all. The simple "case _:" case is using
_ the same way that "case (Color.SCARLETT, _):" is.
ChrisA
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