On 11/27/2017 10:51 AM, Guido van Rossum wrote:
Following up on this subthread (inline below).
Didn't we at one point have something like
isinstance(other, self.__class__) and fields(other) == fields(self) and
<all individual fields match>
(plus some optimization if the types are identical)?
That feels ideal, because it means you can subclass Point just to add
some methods and it will stay comparable, but if you add fields it will
always be unequal.
One thing this doesn't let you do is compare instances of two different
subclasses of a base type:
@dataclass
class B:
i: int
@dataclass
class C1(B): pass
@dataclass
class C2(B): pass
You can't compare C1(0) and C2(0), because neither one is an instance of
the other's type. The test to get this case to work would be expensive:
find the common ancestor, and then make sure no fields have been added
since then. And I haven't thought through multiple inheritance.
I suggest we don't try to support this case.
Eric.
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