Chapter 19

Type Parameterization

In this chapter, we'll explain the details of type parameterization in Scala. Along the way we'll demonstrate some of the techniques for information hiding introduced in Chapter 13 by means of a concrete example: the design of a class for purely functional queues. We're presenting type parameterization and information hiding together, because information hiding can be used to obtain more general type parameterization variance annotations.

Type parameterization allows you to write generic classes and traits. For example, sets are generic and take a type parameter: they are defined as Set[T]. As a result, any particular set instance might be a Set[String], a Set[Int], etc.—but it must be a set of something. Unlike ...

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