there is something i don’t understand. is everything non-nullable by default (unless i use “?”) or i...

# getting-started

[Laurent Laborde]

there is something i don’t understand. is everything non-nullable by default (unless i use “?”) or is there something specific to write to ensure that something can’t be nulled ?

[AndreyVanDenHaag]

There is no default. Without ? you explicitly make it non-nullable.

[ephemient]

in Kotlin, a concrete type written as String is non-nullable, String? is nullable. types coming from Java have unknown nullability unless they have a recognized annotation, https://kotlinlang.org/docs/java-interop.html#null-safety-and-platform-types

[ephemient]

if you have a generic type <T> in Kotlin, without further constraints, it does not have a specified nullability. you can use a constraint such as <T : Any> to ensure it is always a non-nullable type, or write T? or T & Any (the latter is new in Kotlin 1.7) to make specific use-sites nullable or non-nullable

[Stephan Schroeder]

make sure to know about platform types to understand why extra attention is required when interacting with java code (nulls might leak into your non-nullable variables when interacting with Java). https://kotlinlang.org/docs/java-interop.html#null-safety-and-platform-types

[Laurent Laborde]

i’ve read the documentation but somehow, compared to other part of the documentation, this one isn’t very beginner friendly. i found a lot of explanation that use String as an exemple, but i wasn’t sure if String was a specific case or if everything was non-nullable unless specified otherwise.

[Laurent Laborde]

(+ some exception with interop)

[Laurent Laborde]

anyway, you answered my question. thank you