reflection - Scala weird behavior for type conversion in generic function -

could explain why happens?

scala> def as[t](v: any) = try(v.asinstanceof[t]) as: [t](v: any)scala.util.try[t]  scala> as[int]("hello") res0: scala.util.try[int] = success(hello)  scala> res0.map(_ + 1) res1: scala.util.try[int] = failure(java.lang.classcastexception: java.lang.string cannot cast java.lang.integer) 

it's not boxing because use own type instead of int , behaves same way.

doesn't seem by-name parameter either, because replace try option , same.

i'm guessing it's erasure, maybe give detailed explanation?

it's in scaladoc:

note success of cast @ runtime modulo scala's erasure semantics. therefore expression 1.asinstanceof[string] throw classcastexception @ runtime, while expression list(1).asinstanceof[list[string]] not. in latter example, because type argument erased part of compilation not possible check whether contents of list of requested type.

so, because t erased, try(v.asinstanceof[t]) not throw classcastexception, because far jvm knows, have try[any]. try treat contained type int, trigger exception.