Scala | Upper bound - GeeksforGeeks

Scala has some restrictions on the Type Parameters or Type Variable i.e, (type bound) and Upper bound is one of them. By implementing Type Bounds, We can explicate the restraints of a Type Variable, these type bound restricts the definite values of the type variables and discloses more details about the member of these types. Upper bound is defined on type parameters.
Syntax

[T <: S]

Where, ‘T’ is a type parameter and ‘S’ is a type“[T <: S]” means this Type Parameter T must be either same as S or Sub-Type of S.

Let’s understand upper bound with example.
Example

// Scala Program To Demonstrate Scala Upper Bound 
class GeeksforGeeks 
class Author extends GeeksforGeeks 
class Geeks extends Author 
  
class ComputerSciencePortal 
{ 
    // Declaration of upper bound 
    def display [T <: Author](d : T) 
    { 
        println(d) 
    } 
} 
  
// Object created 
object ScalaUpperBounds 
{ 
    // Driver code 
    def main(args: Array[String]) 
    { 
  
        val geeksforgeeks = new GeeksforGeeks 
        val author = new Author 
        val geeks = new Geeks 
  
        val computerscienceportal = new ComputerSciencePortal 
  
    // computerscienceportal.display(geeksforgeeks) 
    computerscienceportal.display(geeks) 
    computerscienceportal.display(author) 
    } 
} 

Output:

Geeks@506e1b77
Author@4fca772d

Here, Upper bound is defined in class ComputerSciencePortal, and GeeksforGeeks is the Super class of Author so its not accepted.

Example

// Scala Program To Demonstrate Scala Upper Bound 
class  Principal 
class Teacher extends Principal 
class Student extends Teacher 
  
class School 
{ 
    // Declaration of upper bound 
    def display [T <: Teacher](t: T) 
    { 
        println(t) 
    } 
} 
  
// Object created 
object ScalaUpperBounds 
{ 
    // Driver code 
    def main(args: Array[String]) 
    { 
        // Defined new variable 
        val principal = new Principal 
        val teacher = new Teacher 
        val student = new Student 
  
        val school = new School 
          
        // school.display(principal) 
        school.display(teacher) 
        school.display(student) 
  } 
} 

Output:

Teacher@506e1b77
Student@4fca772d

Here, we have defined Upper bound in Class School i.e, [T <: Teacher] which implies that display method accepts Teacher class object or subclass of it (i.e. Student) which means that super class of Teacher will not be accepted. So, if Super class of Teacher i.e, Principal is not commented then it will show type mismatch error.

My Personal Notes

Recommended Posts: