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Upper Bound in Scala

By IncludeHelp Last updated : November 16, 2024

Upper bound

The Upper bound is a type bound in Scala which is used on type variables in order to analyze the type condition bounding these type values.

Syntax

[T <: N]

Here, T is a type parameter; S is a type.

The upper bound implements that T can either be sub-type of S or can be of the type same as S.

Example of Upper Bound

abstract class Animals {
  def voice: String
}

class Wild extends Animals {
  override def voice: String = "!"
}

class Lion extends Wild {
  override def voice: String = "Roars!"
}

class Forest {
  def display[T <: Wild](d: T): Unit = { 
    println(d.voice) 
  } 
}

object ScalaUpperBounds {
  def main(args: Array[String]): Unit = {
    val wildAnimal = new Wild
    val lion = new Lion
    val forest = new Forest
    
    forest.display(wildAnimal)
    println(wildAnimal.voice)

    forest.display(lion)
    println(lion.voice)
  } 
}

Output

!
!
Roars!
Roars!