Fix checking whether types are instantiable. #668
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The logic for checking aginst the self type was wrong, as demonstrated by pos/checkInstantiable.scala.
| if (selfType.exists && !(tp <:< selfType)) | ||
| // Create a synthetic singleton type instance, and check whether | ||
| // it conforms to the self type of the class as seen from that instance. | ||
| val stp = SkolemType(tp) |
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Am I right in assuming that this is similar to tp.narrow in scalac?
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In those terms, this LGTM, although I must admit I wouldn't have been able to come up with this formulation myself.
scala> class LS[T] { self: LS[T] => }
defined class LS
scala> val cls = symbolOf[LS[_]]
cls: $r.intp.global.TypeSymbol = class LS
scala> val tp = typeOf[LS[Any]]
tp: $r.intp.global.Type = LS[Any]
scala> val stp = tp.narrow
stp: $r.intp.global.Type = <refinement>.type
scala> val selfType = cls.selfType.asSeenFrom(stp, cls)
selfType: $r.intp.global.Type = LS[Any]
scala> stp <:< selfType
res7: Boolean = true
vs
scala> class LS[T] { self: LS[T with String] => }
defined class LS
scala> val tp = typeOf[LS[Any]]
tp: $r.intp.global.Type = LS[Any]
scala> val cls = symbolOf[LS[_]]
cls: $r.intp.global.TypeSymbol = class LS
scala> val selfType = cls.selfType.asSeenFrom(stp, cls)
selfType: $r.intp.global.Type = LS[T with String]
scala> stp <:< selfType
res8: Boolean = false
|
@retronym SkolemType is indeed a cheaper version of narrow. It took some iterations and dead ends to come up with the current formulation of checkInstantiable. |
odersky
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Jun 22, 2015
Fix checking whether types are instantiable.
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The logic for checking aginst the self type was wrong, as demonstrated
by pos/checkInstantiable.scala. Review by @retronym.