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Kotlin null-safety — what do `?`, `?.`, `?:`, and `!!` mean?

Tags

#null-safety#elvis#nullable

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Answer

`T?` is a nullable type, `?.` is a safe call, `?:` (Elvis) provides a default, and `!!` asserts non-null (throws if it’s null).

val name: String? = null
val len = name?.length ?: 0
// val crash = name!!.length // throws if name is null

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