Knoldus Blogs

Scala Variances: Covariance, Contravariance, and Invariance

July 14, 2021July 14, 2021Scala, Tech BlogsContravariance, Covariance, invariance, scala, Variance

Reading Time: 4 minutes 1. Variance Variance is the interconnection of subtyping relationship between complex types and their component types. Variance is all about sub-typing. It tells us if a type constructor is a subtype of another type constructor. Variance defines inheritance relationships of parameterized types(types that have parameters within them). Sub-Typing Every programming language supports the concept of types. Types give information about how to handle values at Continue Reading

Scala: Generic classes and Variance

April 15, 2019Functional Programming, ScalaContravariance, Covariance, generic classes, generics, inheritance, invariance, Variance

Reading Time: 4 minutes Generic classes are classes which take a type as a parameter. This means, one class can be used with different types without actually writing down it multiple times. They are particularly useful for collection classes. Defining a generic class: Generic classes take a type as a parameter within square brackets [ ]. One convention is to use the letter A as type parameter identifier, though Continue Reading

Back2Basics: Demystifying Variance

May 3, 2018May 9, 2018Scala, Tutorialback2basics, Contravariance, Covariance, Functional Programming, learning, programming, scala, scalafp, Upper Bound, Variance

Reading Time: 5 minutes In this blog, we will explore types of variances in Scala. In-variance Co-variance Contra-variance First, let’s talk about Types in Scala. scala> import java.util.ArrayList scala> var ref1: Any = “Hi” ref1: Any = Hi scala> var ref2: String = “Hi” ref2: String = Hi scala> ref1 = ref2 ref1: Any = Hi In the above example, ref1 is of type Any and ref2 is of Continue Reading

Back2Basics: Scala Type System in Depth

April 16, 2018April 19, 2018Scalaback2basics, Bounds, Contravariance, Covariance, Type paramterization, Variance

Reading Time: 5 minutes In this blog, I will put emphasis on the power and awesomeness of the Scala Type System. Also, I will try to reiterate that it is not difficult or complicated as perceived. In layman terms, the Scala Type system helps us keep the code tidy and type safe. So in this blog, I shall take you through the following : Parameterized types In-Variance Co-Variance Contra-Variance