Reified Type Parameters
We'll cover the following
Why reified type parameters are needed
When using generics in Java we sometimes get into smelly situations where we have to pass Class<T>
parameters to functions. This becomes necessary when the specific parametric type is needed in a generic function but the type details are lost due to Java’s type erasure. Kotlin removes this smell with reified type parameters.
To get a clear understanding of reification, we’ll first explore some verbose and unpleasant code where we pass the class details as a parameter to a function, and then we’ll refactor the code to use type reification.
Suppose we have a base class Book
and a couple of derived classes, like so:
// reifiedtype.kts
abstract class Book(val name: String)
class Fiction(name: String) : Book(name)
class NonFiction(name: String) : Book(name)
Here’s a list that includes different kinds of books:
// reifiedtype.kts
val books: List<Book> = listOf(
Fiction("Moby Dick"), NonFiction("Learn to Code"), Fiction("LOTR"))
The list contains a mixture of Fiction
and NonFiction
instances in the List<Book>
. Now, suppose we want to find the first instance of a particular type, either a Fiction
or a NonFiction
from the list. We may write a function like this in Kotlin, much like how we’d write it in Java:
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