@implicitNotFound(msg = "No TypeTest available for [${S}, ${T}]") trait TypeTest[-S, T] extends Serializable

A TypeTest[S, T] contains the logic needed to know at runtime if a value of type S can be downcasted to T.

If a pattern match is performed on a term of type s: S that is uncheckable with s.isInstanceOf[T] and the pattern are of the form:

  • t: T

  • t @ X() where the X.unapply has takes an argument of type T then a given instance of TypeTest[S, T] is summoned and used to perform the test.

class Object
trait Matchable
class Any

Value members

Abstract methods

def unapply(x: S): Option[x & T]

A TypeTest[S, T] can serve as an extractor that matches only S of type T.

The compiler tries to turn unchecked type tests in pattern matches into checked ones by wrapping a (_: T) type pattern as tt(_: T), where tt is the TypeTest[S, T] instance. Type tests necessary before calling other extractors are treated similarly. SomeExtractor(...) is turned into tt(SomeExtractor(...)) if T in SomeExtractor.unapply(x: T) is uncheckable, but we have an instance of TypeTest[S, T].