How to access "overridden" inner class in Scala?
I have two traits, one extending the other, each with an inner class, one extending the other, with the same names:
trait A {
class X {
def x() = doSomething()
}
}
trait B exte开发者_运维技巧nds A {
class X extends super.X {
override def x() = doSomethingElse()
}
}
class C extends B {
val x = new X() // here B.X is instantiated
val y = new A.X() // does not compile
val z = new A.this.X() // does not compile
}
How do I access A.X
class in the C
class's body? Renaming B.X
not to hide A.X
is not a preferred way.
To make things a bit complicated, in the situation I have encountered this problem the traits have type parameters (not shown in this example).
trait A {
class X {
def x() = "A.X"
}
}
trait B extends A {
class X extends super.X {
override def x() = "B.X"
}
}
class C extends B {
val self = this:A
val x = new this.X()
val y = new self.X()
}
scala> val c = new C
c: C = C@1ef4b
scala> c.x.x
res0: java.lang.String = B.X
scala> c.y.x
res1: java.lang.String = A.X
For those interested in this exotic issue, I have discovered it works also as a return value of a function. Since my traits A and B have type parameters, it should lead to more concise code:
trait A[T, U, V] {
class X {
def x() = "A.X"
}
def a = this:A[T, U, V]
}
trait B[T, U, V] extends A[T, U, V] {
class X extends super.X {
override def x() = "B.X"
}
}
class C extends B[SomeClass, SomeOtherClass, ThirdOne] {
val aVerbose = this:A[SomeClass, SomeOtherClass, ThirdOne] // works but is a bit ugly
val aConcise = a
val x = new this.X()
val y = new aVerbose.X()
val z = new aConcise.X()
}
scala> val c = new C()
c: C = C@1e852be
scala> c.x.x()
res2: java.lang.String = B.X
scala> c.y.x()
res3: java.lang.String = A.X
scala> c.z.x()
res4: java.lang.String = A.X
精彩评论