How to Overcome Type Erasure in Scala?

Type erasure may provide challenges in Scala, particularly when dealing with generics. Type tags and manifests are a means to prevent type erasure. By preserving type information during runtime, these approaches let you operate with genuine types as opposed to erased types.

What is Type Erasure?

Scala, like Java, is built on the JVM and hence has the same type of erasure problem. Type parameters are removed during compilation, which makes using generic types at runtime challenging. Activities like pattern matching and reflection may be hampered by this restriction.

Overcoming Type Erasure

Using Type Tags

Type tags may be imported from scala.reflect and are a component of the Scala standard library. They provide a method for runtime access to type information.

Below is the Scala program to overcome type erasure using type tags:

import scala.reflect.runtime.universe._

def example[T: TypeTag](list: List[T]): Unit = {
  val tpe = typeOf[T]
  println(s"Type is $tpe")
}

example(List(1, 2, 3))  
example(List("a", "b", "c"))  

Output:

This example function outputs the type of T after accepting a List[T]. The TypeTag context bound T: TypeTag guarantees runtime availability of the type tag.

Using Manifests

Using manifests, which are currently deprecated but still functional, provides an additional strategy.

Below is the Scala program to overcome type erasure using manifests:

import scala.reflect.Manifest

def example[T: Manifest](list: List[T]): Unit = {
  val man = manifest[T]
  println(s"Type is $man")
}

example(List(1, 2, 3))  
example(List("a", "b", "c"))  

Output:

By giving you access to type information at runtime, both of these techniques assist you in overcoming type erasure and let you to carry out activities that type erasure would otherwise prevent.

Using ClassTag

A variant of TypeTag designed specifically for arrays, ClassTag is likewise included in the scala.reflect package. Accurate handling of generic arrays is made possible by its ability to capture the runtime class of the type argument.

Below is the Scala program to overcome type erasure using classtag:

import scala.reflect.ClassTag

def example[T: ClassTag](array: Array[T]): Unit = {
  val tpe = implicitly[ClassTag[T]].runtimeClass
  println(s"Type of array elements: $tpe")
}

// Example
example(Array("a", "b", "c"))

Output:

Using WeakTypeTag

A component of the scala.reflect.runtime.universe package, WeakTypeTag handles more complicated situations involving existential and higher-kinded types than TypeTag. It has a poor ability to record type information, hence in certain circumstances it may not resolve completely.

Below is the Scala program to overcome type erasure using weaktype tag:

import scala.reflect.runtime.universe._

def example[T: WeakTypeTag](value: T): Unit = {
  val tpe = weakTypeOf[T]
  println(s"Weak type of value: $tpe")
}

// Example
example(List(1, 2, 3))

Output: