Kotlin - equivalence to Swift's combination of "if let + cast"

Question

I'm trying to find out how to achieve the combination of "if let + cast" in kotlin:

in swift:

if let user = getUser() as? User {    // user is not nil and is an instance of User } 

I saw some documentation but they say nothing regarding this combination

https://medium.com/@adinugroho/unwrapping-sort-of-optional-variable-in-kotlin-9bfb640dc709 https://kotlinlang.org/docs/reference/null-safety.html

Answer 1

One option is to use a safe cast operator + safe call + let:

(getUser() as? User)?.let { user ->     ... } 

Another would be to use a smart cast inside the lambda passed to let:

getUser().let { user ->     if (user is User) {         ...     } } 

But maybe the most readable would be to just introduce a variable and use a smart cast right there:

val user = getUser() if (user is User) {     ... } 

Answer 2

Kotlin can automatically figure out whether a value is nil or not in the current scope based on regular if statements with no need for special syntax.

val user = getUser()  if (user != null) {     // user is known to the compiler here to be non-null } 

It works the other way around too

val user = getUser()  if (user == null) {     return }  // in this scope, the compiler knows that user is not-null  // so there's no need for any extra checks user.something