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author | Jason Zaugg <jzaugg@gmail.com> | 2015-03-17 18:14:08 -0700 |
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committer | Jason Zaugg <jzaugg@gmail.com> | 2015-03-17 18:44:37 -0700 |
commit | d0181ab3810f1e063b33e79b43f183a098de2aab (patch) | |
tree | ef6db3de02c81de1aef428debec5b34b96e35348 /test | |
parent | fa33395a25c87115c910e8d4a4124aee6134062b (diff) | |
download | scala-d0181ab3810f1e063b33e79b43f183a098de2aab.tar.gz scala-d0181ab3810f1e063b33e79b43f183a098de2aab.tar.bz2 scala-d0181ab3810f1e063b33e79b43f183a098de2aab.zip |
Resurrect a test for type inference
This test was removed in ... when case class extension was disallowed.
But the intent of the test was actually to exercise a path through
type inference, described in `Infer#exprTypeArgs`.
When I remove that special case, the test still fails:
```
test/files/pos/jesper.scala:29: error: No implicit view available from Pair.Cons[Int,Pair.Cons[Boolean,Pair.End]] => Boolean.
val x2 : Boolean = p.find[Boolean] // Doesn't compile
^
one error found
```
This special case is important to understand when deciphering
the inference in this program:
```
object Test {
trait Cov[+A]
def cov[A](implicit ev: Cov[A]): A = ???
implicit def covImp[A]: Cov[A] = ???
trait Inv[A]
def inv[A](implicit ev: Inv[A]): A = ???
implicit def invImp[A]: Inv[A] = ???
trait Con[-A]
def con[A](implicit ev: Con[A]): A = ???
implicit def conImp[A]: Con[A] = ???
cov : String // (Test.this.cov[String](Test.this.covImp[Nothing]): String);
// (Test.this.cov[Nothing](Test.this.covImp[Nothing]): String) (or, without the special case in exprTypeArgs)
inv : String // (Test.this.inv[Nothing](Test.this.invImp[Nothing]): String);
con : String // (Test.this.con[Any](Test.this.conImp[Any]): String)
}
```
Diffstat (limited to 'test')
-rw-r--r-- | test/files/pos/jesper.scala | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/test/files/pos/jesper.scala b/test/files/pos/jesper.scala new file mode 100644 index 0000000000..82623e4a24 --- /dev/null +++ b/test/files/pos/jesper.scala @@ -0,0 +1,30 @@ +object Pair { + sealed trait Pair { + type First + type Second <: Pair + } + + case class End() extends Pair { + type First = Nothing + type Second = End + + def ::[T](v : T) : Cons[T, End] = Cons(v, this) + } + + object End extends End() + + final case class Cons[T1, T2 <: Pair](_1 : T1, _2 : T2) extends Pair { + type First = T1 + type Second = T2 + + def ::[T](v : T) : Cons[T, Cons[T1, T2]] = Cons(v, this) + def find[T](implicit finder : Cons[T1, T2] => T) = finder(this) + } + + implicit def findFirst[T1, T2 <: Pair] : Cons[T1, T2] => T1 = (p : Cons[T1, T2]) => p._1 + implicit def findSecond[T, T1, T2 <: Pair](implicit finder : T2 => T) : Cons[T1, T2] => T = (p : Cons[T1, T2]) => finder(p._2) + + val p : Cons[Int, Cons[Boolean, End]] = 10 :: false :: End +// val x : Boolean = p.find[Boolean](findSecond(findFirst)) + val x2 : Boolean = p.find[Boolean] // Doesn't compile +} |