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jspahrsummers / adt

Algebraic data types for Python (experimental, not actively maintained)
MIT License
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Implement hash function for ADTs #32

Open mikelynch opened 4 years ago

mikelynch commented 4 years ago

According to the Python documentation:

The only required property is that objects which compare equal have the same hash value

At the moment, this isn't the case:

from adt import adt, Case

a1 = "abc"

a2 = "ab"
a2 += "c"

assert a1 == a2
assert hash(a1) == hash(a2)

@adt
class OptionStr:
    SOME: Case[str]
    NONE: Case

b1 = OptionStr.SOME(a1)
b2 = OptionStr.SOME(a2)

assert b1 == b2
assert hash(b1) == hash(b2)  # Fails

It looks like the fix is to add an additional function in adt/decorator.py – are there any subtleties that complicate that?

jspahrsummers commented 4 years ago

Thanks for the bug report! I agree this is a problem.

IIRC this should be a relatively straightforward change, implemented in the style of __eq__. I'm not sure there are any subtleties that wouldn't also apply to equality.

I'd be happy to review a pull request if anyone would like to submit a patch.