Generics
- type invariance - strict type
- covariance - permit a derived class of a parametric type
- in java
<? extends T> - in kotlin
Array<out SuperClass>- allows reading
- in java
- contravariance - permit a super class of a parametric type
- in java
<? super T> - in kotlin
Array<in SuperClass>- allows writing
- in java
- star projection - permit only reads
Array<*>
Kotlin allows both use-site variance and declaration-site variance.
Parametric Type Constraints - where
fun <T: AutoCloseable> useAndClose(input: T) = input.close() // T should confirm to one type
// T confirm to multiple types
fun <T> useAndClose(input: T) where T: AutoCloseable, T: Appendable {
input.append("something")
input.close()
}