1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
|
import scala.reflect.runtime.universe._
// inference illuminator
object Test {
class D1[T1 : TypeTag, T2 <: T1 : TypeTag](x: T1) { println(typeOf[(T1, T2)]) }
class D2[T1 : TypeTag, T2 >: T1 : TypeTag](x: T1) { println(typeOf[(T1, T2)]) }
class D3[+T1 : TypeTag, T2 <: T1 : TypeTag](x: T1) { println(typeOf[(T1, T2)]) }
class D4[-T1 : TypeTag, T2 >: T1 : TypeTag](x: T1) { println(typeOf[(T1, T2)]) }
class E1[T1 : TypeTag, T2 <: T1 : TypeTag](x: D1[T1, T2]) { println(typeOf[(T1, T2)]) }
class E2[T1 : TypeTag, T2 >: T1 : TypeTag](x: D2[T1, T2]) { println(typeOf[(T1, T2)]) }
class E3[+T1 : TypeTag, T2 <: T1 : TypeTag](x: D3[T1, T2]) { println(typeOf[(T1, T2)]) }
class E4[-T1 : TypeTag, T2 >: T1 : TypeTag](x: D4[T1, T2]) { println(typeOf[(T1, T2)]) }
def main(args: Array[String]): Unit = {
// WHY YOU NO LIKE NOTHING SO MUCH SCALAC?
val d1 = new D1(5)
val d2 = new D2(5)
val d3 = new D3(5)
val d4 = new D4(5)
new E1(d1) // fails
new E2(d2)
new E3(d3) // fails
new E4(d4)
}
// found : Test.D1[Int,Nothing]
// required: Test.D1[Int,T2]
// Note: Nothing <: T2, but class D1 is invariant in type T2.
// You may wish to define T2 as +T2 instead. (SLS 4.5)
// new E1(d1)
// ^
// test/pending/pos/inference.scala:22: error: type mismatch;
// found : Test.D3[Int,Nothing]
// required: Test.D3[Int,T2]
// Note: Nothing <: T2, but class D3 is invariant in type T2.
// You may wish to define T2 as +T2 instead. (SLS 4.5)
// new E3(d3)
// ^
// two errors found
}
|
