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class A {
trait Container[+T]
trait Template[+CC[X] <: Container[X]]
class C1[T] extends Template[C1] with Container[T]
class C2[T] extends Template[C2] with Container[T]
/** Target expression:
* List(new C1[String], new C2[String])
*/
// Here's what would ideally be inferred.
//
// scala> :type List[Template[Container] with Container[String]](new C1[String], new C2[String])
// List[Template[Container] with Container[java.lang.String]]
//
// Here's what it does infer.
//
// scala> :type List(new C1[String], new C2[String])
// <console>:8: error: type mismatch;
// found : C1[String]
// required: Container[String] with Template[Container[Any] with Template[Container[Any] with Template[Any] with ScalaObject] with ScalaObject] with ScalaObject
// List(new C1[String], new C2[String])
// ^
//
// Simplified, the inferred type is:
//
// List[Container[String] with Template[Container[Any] with Template[Container[Any] with Template[Any]]]
//
// *** Update 2/24/2012
//
// Hey, now there are polytypes in the inferred type.
// Not sure if that is progress or regress.
//
// test/pending/pos/those-kinds-are-high.scala:36: error: type mismatch;
// found : C1[String]
// required: ScalaObject with Container[String] with Template[ScalaObject with Container with Template[ScalaObject with Container with Template[[X]Container[X]]]]
// def fFail = List(new C1[String], new C2[String])
// ^
// test/pending/pos/those-kinds-are-high.scala:36: error: type mismatch;
// found : C2[String]
// required: ScalaObject with Container[String] with Template[ScalaObject with Container with Template[ScalaObject with Container with Template[[X]Container[X]]]]
// def fFail = List(new C1[String], new C2[String])
// ^
// two errors found
/** Working version explicitly typed.
*/
def fExplicit = List[Template[Container] with Container[String]](new C1[String], new C2[String])
// nope
def fFail = List(new C1[String], new C2[String])
}
trait Other {
trait GenBar[+A]
trait Bar[+A] extends GenBar[A]
trait Templ[+A, +CC[X] <: GenBar[X]]
abstract class CC1[+A] extends Templ[A, CC1] with Bar[A]
abstract class CC2[+A] extends Templ[A, CC2] with Bar[A]
// Compiles
class A1 {
abstract class BarFactory[CC[X] <: Bar[X]]
def f(x: Boolean) = if (x) (null: BarFactory[CC1]) else (null: BarFactory[CC2])
}
// Fails - only difference is CC covariant.
class A2 {
abstract class BarFactory[+CC[X] <: Bar[X]]
def f(x: Boolean) = if (x) (null: BarFactory[CC1]) else (null: BarFactory[CC2])
// c.scala:23: error: kinds of the type arguments (Bar with Templ[Any,Bar]) do not conform to the expected kinds of the type parameters (type CC) in class BarFactory.
// Bar with Templ[Any,Bar]'s type parameters do not match type CC's expected parameters:
// <empty> has no type parameters, but type CC has one
// def f(x: Boolean) = if (x) (null: BarFactory[CC1]) else (null: BarFactory[CC2])
// ^
// one error found
}
// Compiles - CC contravariant.
class A3 {
abstract class BarFactory[-CC[X] <: Bar[X]] // with Templ[X, CC]]
def f(x: Boolean) = if (x) (null: BarFactory[CC1]) else (null: BarFactory[CC2])
// c.scala:23: error: kinds of the type arguments (Bar with Templ[Any,Bar]) do not conform to the expected kinds of the type parameters (type CC) in class BarFactory.
// Bar with Templ[Any,Bar]'s type parameters do not match type CC's expected parameters:
// <empty> has no type parameters, but type CC has one
// def f(x: Boolean) = if (x) (null: BarFactory[CC1]) else (null: BarFactory[CC2])
// ^
// one error found
}
}
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