Generics: Variance and Constraints of Parametric Types
The desire to reuse code shouldn’t come at a cost of compromising type safety. Generics bring a nice balance to this issue. With generics you can create code that can be reused for different types. At the same time, the compiler will verify that a generic class or a function isn’t used with unintended types. We’ve enjoyed a fairly good amount of type safety with generics in Java. So, you may wonder, what could Kotlin possibly provide to improve? It turns out, quite a bit.
By default, in Java, generics impose type invariance—that is, if a generic function expects a parametric type T, you’re not allowed to substitute a base type of T or a derived type of T; the type has to be exactly the expected ...
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