Variance In Scala

Variance In Scala

Anish Kumar Anish Kumar

Anish Kumar

Scala | Cat | Akka | Spark | ElasticSearch | Kafka

发布日期: 2024年5月8日
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1. All values have a type

2. Types have supertype relationships up to Any

3. Types have subtype relationships down to Nothing

4. References can store subclass instances (polymorphism)

Variance example: List[T]

  1. Container: List is a container of type List.
  2. Content: the content of List(Container) will be type T.
  3. A container can store the content.

In general, there are three modes of variance:

  • invariant—the default, written like List[T]
  • covariant—annotated with a +, written like List[+T]
  • contravariant—annotated with a -, written like List[-T]

To understand Variance, we must consider the container and the content.

Polymorphism: We can store the child class in the parent class reference.

Considering the following relation let's understand variance:

Example 1: In-Variance

Example 2: Co-Variance

Example 3: Contra-Variance

GitHub: https://github.com/anish-diliyan/core-scala/tree/master/src/main/scala/generics



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