Simplify Collection. #10450
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Simplify Collection. #10450
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Collection and its subclasses are now just new-types for tuple removing the previously awkward `dependencies` field exposed for the engine. The engine is updated to handle these Collections as Iterable Python objects when attempting to collect their contained values.
Test failures revealed isinstance for types derived from tuple behaves unexpectedly under Python3.6. Although this can be worked around by saving off the mro in __init_subclass__ and using that to perform a custom isinstance check, more investigation indicated two aspects of the status quo were undesirable: 1. By returning NotImplemented we left equality up to foreign types to decide. 2. The intended use of Collection subtypes is for the engine, which treats all types as distinct; yet we would compare subtypes as equal. As such implement exact type match based equality and document this.
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PTAL. So ... isinstance(..., subclass-of-tuple) behaves not like you'd expect in Python3.6. Works fine in 3.7 and 3.8. I spent a good chunk of time debugging this and then coming up with a performant workaround, but then realized we should have just been checking for identical types anyhow al along. So I switched to that and that semantic change probably deserves another look / more brains considering. |
Eric-Arellano
approved these changes
Jul 26, 2020
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Collection and its subclasses are now just new-types for tuple removing
the previously awkward
dependenciesfield exposed for the engine. Theengine is updated to handle these Collections as Iterable Python
objects when attempting to collect their contained values.