Kotlinhard

What is a value class (`@JvmInline`) and why would you use it?

Tags

#value-class#type-safety#domain

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Answer

A value class wraps a single value to add type-safety without runtime object overhead in many cases (it can be inlined). It’s useful for strong domain types like `UserId` vs `String`.

@JvmInline
value class UserId(val value: String)

fun loadUser(id: UserId) = id.value

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