On 12/8/2017 9:14 PM, Nathaniel Smith wrote:
On Dec 7, 2017 12:49, "Eric V. Smith" <e...@trueblade.com
<mailto:e...@trueblade.com>> wrote:
The reason I didn't include it (as @dataclass(slots=True)) is
because it has to return a new class, and the rest of the dataclass
features just modifies the given class in place. I wanted to
maintain that conceptual simplicity. But this might be a reason to
abandon that. For what it's worth, attrs does have an
@attr.s(slots=True) that returns a new class with __slots__ set.
They actually switched to always returning a new class, regardless of
whether slots is set:
https://github.com/python-attrs/attrs/pull/260
In the end, it looks like that PR ended up just refactoring things, and
the decision to always return a new class was deferred. I still haven't
finished evaluating exactly what the refactoring does, though.
Eric.
You'd have to ask Hynek to get the full rationale, but I believe it was
both for consistency with slot classes, and for consistency with regular
class definition. For example, type.__new__ actually does different
things depending on whether it sees an __eq__ method, so adding a method
after the fact led to weird bugs with hashing. That class of bug goes
away if you always set up the autogenerated methods and then call
type.__new__.
They have a bunch of test cases that I'll have to review, too.
Eric.
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