a question, how to write `if (a.city != null) city...

# getting-started

[Łukasz Gendek]

a question, how to write if (a.city != null) city = a.city!! in a kotlin idiomatic way?

[Sam]

Well, there’s always a.city?.let { city = it }. Not sure how much I like it, though.

[Goetz Markgraf]

The first one is dangerous because in a multithreaded app a.city could have been mutated after the check but before the access, resulting in a NullPointerException.

The suggestion by @Sam is better

[Sam]

You could also write city = a.city ?: city, which should achieve the same effect as long as reassigning city doesn’t have side effects

[Goetz Markgraf]

Best not to use mutable fields or variables altogether!