Allow to declare directly `val` in the `if` statement and use in body

Language Design
1

First of all, Kotlin is awesome!

Second, it’d be cool if we could have something similar to smart cast, that is declaring a val (thread safe) inside the if statement and use it directly in the body

if( val email = client?.personalInfo?.email != null && message!=null) mailer.sendMessage(email, message)

1 Like
2

I’m not really a language expert, but that just seems harder to read while you’re only saving one line of code. I’d prefer putting the email initialization right above that.

3

You can use the let function for this purpose:

client?.personalInfo?.email?.let { email -> 
  if (message != null) mailer.sendMessage(email, message)
}
3 Likes
4

That would be wonderful:

if (val value = this.Value; value is Type) {

}

5

Just use a let:

this.Value.let { value ->
  if (value !is Type) return@let
  ...
}
6

In this specific case, I would write:

this.Value
  .let{ it as? Type }
  ?.let { value -> ... }
7

Or even:

(this.Value as? Type)?.let { value ->
  ...
}
1 Like
8

Or even

val value = this.Value; if (value is Type) {
    …
}

I am very much in favor of preferring the most basic syntax unless there are significant advantages to the more creative alternatives.

1 Like
9

How about a little helper function?

inline fun <reified T> Any.ifType(crossinline body : (T) -> Unit) {
    if (this is T) {
        body(this)
    }
}

Usage: this.Value.ifType<Type>{ v -> ... }