Hello,
Le 15/07/2020 à 13:37, Mohammad Foroughi via Python-Dev a écrit :
> Hi, I had an idea regarding the pattern matching issue of comparing with
> a previous constant variable instead of assigning to a new local
> variable. I'm not sure if this has been brought up before but instead of
> using a symbol with the case statement what if we used a keyword.
>
> [...]
>
> Other ideas for the keyword are "const" or "static" but these 2 are more
> difficult to recognise since they aren't in other parts of python but
> the "global" keyword is already implemented so it would be easy to
> understand.
What about simply "is", which is already a keyword?
AFAIK "is" has no meaning as a prefix operator as of now, so hopefully
it would not make the grammar ambiguous (how can one check that for sure?).
match color:
case is RED:
print("red")
case is BLUE:
print("blue")
case other:
print(f"unknown color {other}")
or with Rhodri James' example:
match value:
case is x:
print("value matches")
case Point(is x, y):
print("value matches x, y captured")
case Line(Point(is x1, y1), Point(x2, is y2)):
print("wouldn't call that pretty, but not ugly either")
Cheers,
Baptiste
P.S.: granted, it could mislead some users into thinking that the
comparison is done with "is" instead of "=="; but then, patterns are
special in many ways, users will have to just learn them…
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