Types overview

In Kotlin, everything is an object in the sense that you can call member functions and properties on any variable. While certain types have an optimized internal representation as primitive values at runtime (such as numbers, characters, and booleans), they appear and behave like regular classes to you.

This section describes the basic types used in Kotlin:

• Numbers and their unsigned counterparts

• Booleans

• Characters

• Strings

• Arrays

To learn about other Kotlin types, such as Nothing, Any, and Unit, look through the Kotlin API reference:

• Any

• Nothing

• Unit

Kotlin also has non-denotable types. They are the types that you can't write directly in the Kotlin code. Instead, the compiler uses them internally, for example, for interoperability with other languages. Kotlin creates non-denotable types to represent type information that is more precise than what Kotlin source syntax allows.

Even though you can't declare non-denotable types yourself, you may encounter them in compiler diagnostics, IDE tooltips, or inferred type displays. Learn more about non-denotable types in:

• Platform types

• Intersection types

• Integer literal types

• Captured types

• Kotlin language specification: Type system