A modern programming language that makes developers happier.

kotlinlang

``` val x : Int? = 5
 // x!! // if uncomment this line there will be no compilation error  
 x + 1 // compilation error as x treated as nullable. I think compiler can 'smart cast' it from initial assignment ```

It was done intentionally, because otherwise there would be no way to opt-out from this smartcast. So the rule is following: smartcasts are inferred from rhs of the `=` only in case of variable assignment, not the variable initialization.
```fun main() {
    val x : Int?
    x = 5
    x + 1 // smartcasted
}```

While trying to check with var faced with strange thing:
```    @Test
    fun test() {
        var x : Int? = 5
        x!!
        x + 1
        x = null
        val y = x + 1 // treat y as String // why?
        println(y) // print null1
    } ```

• `x` smartcasted to `Nothing?`
• `+` resolved to `operator fun String?.plus(other: Any?): String` from stdlib

Because `Nothing?` is subtype of `String?`