Fix #4314: revert changes in #4299 #4333
Conversation
1. ApproximatingTypeMap produces Nothing, which is not what is needed. 2. Avoid blind erasure which lose information about the pattern, see tests/patmat/i4314b.scala
Blind substitution of pattern bound type symbol with WildcardType
will cause t2425.scala fail, as the following holds:
Array[_] <:< Array[Array[_]]
To walkaround the problem, we don't substitute pattern bound symbols
that are immediate parameters to `Array`.
|
test performance with #fast please |
|
performance test scheduled: 1 job(s) in queue, 0 running. |
|
Performance test finished successfully: Visit http://dotty-bench.epfl.ch/4333/ to see the changes. Benchmarks is based on merging with master (ac84047) |
| @@ -356,7 +356,11 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic { | |||
|
|
|||
| val map = new TypeMap { | |||
| def apply(tp: Type) = tp match { | |||
| case tref: TypeRef if isPatternTypeSymbol(tref.typeSymbol) => WildcardType(tref.underlying.bounds) | |||
| case tp @ AppliedType(tycon, args) if tycon.isRef(defn.ArrayClass) => | |||
| // walkaround `Array[_] <:< Array[Array[_]]`, see tests/patmat/t2425.scala | |||
There was a problem hiding this comment.
I don't think this comment is true, the following code doesn't compile:
def foo(x: Array[_]): Array[Array[_]] = xThere was a problem hiding this comment.
The underscore above expands to TypeBounds Array[<: Any :> Nothing] instead of Wildcards.
Here is the subtyping log:
==> Array[(?)] <:< Array[Array[(?)]]
==> scala.type <:< scala.type
<== scala.type <:< scala.type = true
==> Array[(?)] <:< (?)
==> Any <:< Any LoApprox
<== Any <:< Any LoApprox = true
<== Array[(?)] <:< (?) = true
==> (?) <:< Array[(?)]
<== (?) <:< Array[(?)] = true
<== Array[(?)] <:< Array[Array[(?)]] = true
And the behavior can be confirmed from the code in TypeComparer.
But thanks for raising the question, as by using TypeBounds instead WildcardType, we avoid the problem.
There was a problem hiding this comment.
Yes, WildcardType(lo, hi) <:< X is equivalent to lo <:< X, see TypeComparer
| val map = new TypeMap { | ||
| def apply(tp: Type) = tp match { | ||
| case tp @ AppliedType(tycon, args) if tycon.isRef(defn.ArrayClass) => | ||
| // walkaround `Array[_] <:< Array[Array[_]]`, see tests/patmat/t2425.scala |
There was a problem hiding this comment.
s/walkaround/work around/
Use TypeBounds instead of WildcardType. WildcardType has the
following unexpected behavior:
Array[?] <:< Array[Array[?]]
Fix #4314