TypeComparer: delay looking up members of AndTypes #979
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In ParFactory.scala we have checks that look like:
(Foo { type Bar = X }) & (Foo { type Bar = X }) <:< (Foo { type Bar = X })
where `Foo` is a recursive type.
Before this commit, we would first try to check this by looking up `Bar`
in the `AndType` on the left, which means looking it up in both branches
and then merging the result, but the merge requires more subtyping
checks, which in turn require looking up a member inside an `AndType`,
seemingly ad infinitum.
We now avoid this by checking if either branch of the `AndType` on the left
is a subtype of the `RefinedType` on the right before looking up a member
in the `AndType` itself.
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LGTM. I think the logic can be slightly simplified since AndTypes never need an eta lift. I'll take care of that in the higher-kinded PR. |
odersky
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Dec 6, 2015
TypeComparer: delay looking up members of AndTypes
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In ParFactory.scala we have checks that look like:
where
Foois a recursive type.Before this commit, we would first try to check this by looking up
Barin the
AndTypeon the left, which means looking it up in both branchesand then merging the result, but the merge requires more subtyping
checks, which in turn require looking up a member inside an
AndType,seemingly ad infinitum.
We now avoid this by checking if either branch of the
AndTypeon the leftis a subtype of the
RefinedTypeon the right before looking up a memberin the
AndTypeitself.Review by @odersky