Scala | Upper bound
Last Updated :
14 Mar, 2019
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
class GeeksforGeeks
class Author extends GeeksforGeeks
class Geeks extends Author
class ComputerSciencePortal
{
def display [T <: Author](d : T)
{
println(d)
}
}
object ScalaUpperBounds
{
def main(args : Array[String])
{
val geeksforgeeks = new GeeksforGeeks
val author = new Author
val geeks = new Geeks
val computerscienceportal = new ComputerSciencePortal
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
class Principal
class Teacher extends Principal
class Student extends Teacher
class School
{
def display [T <: Teacher](t : T)
{
println(t)
}
}
object ScalaUpperBounds
{
def main(args : Array[String])
{
val principal = new Principal
val teacher = new Teacher
val student = new Student
val school = new School
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.
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