On 2020-07-12 01:32, Chris Angelico wrote:
On Sun, Jul 12, 2020 at 10:30 AM Greg Ewing <greg.ew...@canterbury.ac.nz> wrote:
Just had another thought about marking assignment targets.
The PEP currently forbids repeating bound names in a pattern
to avoid raising expectations that
case Point(x, x):
would match only if the two arguments were equal.
But if assignment targets were marked, we could write this as
case Point(?x, x):
and it would work as expected.
Hang on. Matching happens before assignment, so this should use the
previous value of x for the matching. At least, that's my
understanding. If you do something like:
case Point(x, 2):
it won't assign x unless the second coordinate is 2, right?
Presumably the assumption is that it would use a local dict for binding,
faling back to the actual dict if necessary for lookup, and then update
the actual dict if the match is successful. That way, unsuccessful
matches won't pollute the actual dict.
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