Fix #5844: Use an approximating type map to substitute parent type params #5899
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smarter
requested changes
Feb 13, 2019
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This seems a bit restrictive to me, e.g. the following works in Scala 2:
trait A
trait B[X]{
def m(): X
}
trait C[X] extends B[X with A]
object O{
def m(c: C[_]) = {
val x: A = c.m()
}
}But will fail with this PR. I think we could preserve this by normalizing like this:
X & _ ~> X
X | _ ~> _
|
Thinking about it more, this seems like a job for |
…pe params Actual arguments could be wildcards, which means a normal substitution will not work.
odersky
changed the title
smarter
requested changes
Feb 15, 2019
| @@ -195,4 +195,28 @@ trait Substituters { this: Context => | |||
| final class SubstParamsMap(from: BindingType, to: List[Type]) extends DeepTypeMap { | |||
| def apply(tp: Type): Type = substParams(tp, from, to, this) | |||
| } | |||
|
|
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| /** An approximating substitution that can handle wildcards in the `to` list */ | |||
| final class SubstApproxMap(from: List[Symbol], to: List[Type])(implicit ctx: Context) extends ApproximatingTypeMap { | |||
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The regular SubstBindingMap also extends DeepTypeMap, does this matter here ?
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No, we do not need to substitute ClassInfos here.
Co-Authored-By: odersky <[email protected]>
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Actual arguments could be wildcards, which means a normal substitution will not work.