Conversation
It was 99% dropped, though I forget the reason; part of the issue is that the planned encoding of higher-kinds changed, and there’s a paper on why at the Scala Symposium 2016.
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Wasn't it that type projections were tricky/impossible to prove sound? Curious to know what patterns would have to be dropped if one were to migrate from Scala 2 to Scala 3. (Haven't done much Scala personally)
Type projection _from classes_ are actually unsound (not just an issue with proofs), but projecting types from values is fine. Don't have a ready answer on patterns, we hope none common! (But IIRC the "Scala2" Dotty mode still allows them).
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