Checking structural type in scala by isInstanceOf

Question

I'm just checking structural type equality in scala.

I create a foo instance from annonymous class immediately and a Q type . I intend them to differing with method name, so that hoping them regarded as a different type structurally.

code snippet:

scala> val foo = new {def foo=1}
a: AnyRef{def foo: Int} = $anon$1@3885c37f

scala> type Q = {def q:Unit}
defined type alias Q

scala> foo.isInstanceOf[Q]
<console>:14: warning: a pattern match on a refinement type is unchecked
              foo.isInstanceOf[Q]
                            ^
res55: Boolean = true

The checking returns true.

Q1: I don't understand WHY foo is an instance of Q. That's nonsense. Are not they different in sense of type structure?

Q2: So what is the formal way to checking the structural type?

Answer 1

isInstanceOf is according to class info. In your case, you need type info:

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> val foo = new {def foo=1}
foo: AnyRef{def foo: Int} = $anon$1@15ab47

scala> type Q = {def q:Unit}
defined type alias Q

scala> def getType[T : TypeTag](t: T) = implicitly[TypeTag[T]].tpe
getType: [T](t: T)(implicit evidence$1:reflect.runtime.universe.TypeTag[T])reflect.runtime.universe.Type

scala> getType(foo) =:= typeOf[Q]
res9: Boolean = false