isInstanceOf.scala

trait T
// defined trait T

case class A() extends T
// defined class A

case class B(a: A) extends T
// defined class B

def check[Y <: T](t: T): Boolean = t.isInstanceOf[Y]
// defined function check

val a = A()
// a: A = A()

val b = B(a)
// b: B = B(A())

check[T](a)
check[T](b)
check[A](a)
check[B](b)
// res: Boolean = true <- same result for all above

// ***********
check[A](b)
// res: Boolean = true
// *** `b` is not an instance of A

b.isInstanceOf[A]
// res: Boolean = false
// ***********

// ***********
check[B](a)
// res: Boolean = true
// *** `a` is not an instance of B

// a.isInstanceOf[B]
// res: Boolean = false
// ***********

def checkA(t: T): Boolean = t.isInstanceOf[A]
// defined function checkA

checkA(a)
// res: Boolean = true

checkA(b)
// res: Boolean = false

// *** same for B, `checkB()`