ScalaPatternMatchGenericValueOrCollection.scala

//1. no tag List[T] becomes List at runtime so first case will always work 
object Main {

  def f[T](l: List[T]): Unit = {
    l match {
      case f: List[Float] => println("Floats: " + f)
      case s: List[String] => println("Strings: " + s)
      case i: List[Int] => println("Integers: " + i)
      //      case p: Int if classTag[T] == classTag[Int] => println("Int: " + p)
      case _ => println("error")
    }
  }

  def main(args: Array[String]): Unit = {
    f(List(1, 2, 3))  //floats
    f(List("a", "b")) //floats
    //    f(1)
  }
}


//2. added T:ClassTag becomes List at runtime so first case will always work because we didn't check tag 
object Main {

  def f[T](l: List[T]): Unit = {
    l match {
      case f: List[Float] => println("Floats: " + f)
      case s: List[String] => println("Strings: " + s)
      case i: List[Int] => println("Integers: " + i)
      //      case p: Int if classTag[T] == classTag[Int] => println("Int: " + p)
      case _ => println("error")
    }
  }

  def main(args: Array[String]): Unit = {
    f(List(1, 2, 3))  //floats
    f(List("a", "b")) //floats
    //    f(1)
  }
}

// 3. we add classTag[T]  checks it works as expected, but we got warning

// Warning:(9, 15) non-variable type argument Float in type pattern List[Float] (the underlying of List[Float]) is unchecked since it is eliminated by erasure
      case f: List[Float] if classTag[T] == classTag[Float] => println("Floats: " + f)
...

object Main {
  import scala.reflect.{ClassTag, classTag}

  def f[T: ClassTag](l: List[T]): Unit = {
    l match {
      case f: List[Float] if classTag[T] == classTag[Float] => println("Floats: " + f)
      case s: List[String] if classTag[T] == classTag[String] => println("Strings: " + s)
      case i: List[Int] if classTag[T] == classTag[Int] => println("Ints: " + i)
      //      case p: Int if classTag[T] == classTag[Int] => println("Int: " + p)
      case _ => println("error")
    }
  }

  def main(args: Array[String]): Unit = {
    f(List(1, 2, 3))
    f(List("a", "b"))
    //    f(1)
  }
}

// 4. we can add @unchecked to mute warnings

import scala.reflect.{ClassTag, classTag}

object Main {

  // ClassTag are enough to pattern match top-level class type
  // doesn't know about every field's type, no reflection (no class mirror is build)

  // TypeTag use reflection (build full mirror)

  def f[T: ClassTag](l: List[T]): Unit = {
    l match {
      case f: List[Float@unchecked] if classTag[T] == classTag[Float] => println("Floats: " + f)
      case s: List[String@unchecked] if classTag[T] == classTag[String] => println("Strings: " + s)
      case i: List[Int@unchecked] if classTag[T] == classTag[Int] => println("Ints: " + i)
      //      case p: Int if classTag[T] == classTag[Int] => println("Int: " + p)
      case _ => println("error")
    }
  }

  def main(args: Array[String]): Unit = {
    f(List(1, 2, 3))
    f(List("a", "b"))
    //    f(1)
  }
}


// 5. else we have to check element by element or use reflection (TypeTags) 

def f[T: ClassTag](l: T): Unit = {
  l match {
    // Seq[Any] will be matched to this case because of type erasure,
    // ok only if Seq[TableRow] is possible otherwise whill get runtimeException will handling elements
    case nestedRepeated: Seq[TableRow@unchecked] if classTag[T] == classTag[TableRow] => println("TableRows: " + nestedRepeated)
    case nested: TableRow if classTag[T] == classTag[TableRow] => println("Int: " + nested)
    case _ => println("error")
  }
}