Anyone know why this doesn’t work ```val nullableFoo: Any? = null val nonNullFoo = nullableFoo != nu...

# getting-started

[allan.conda]

Anyone know why this doesn’t work

val nullableFoo: Any? = null
val nonNullFoo = nullableFoo != null
if (nonNullFoo) {
   acceptsNonNullFoo(nullableFoo) // expected Any but is Any?
}

but this works

val nullableFoo: Any? = null
if (nullableFoo != null) {
   acceptsNonNullFoo(nullableFoo)
}

🤔

[Joffrey]

The compiler doesn't analyze the program to this extent (as far as flow analysis is concerned), so it doesn't link the null check on nonNullFoo boolean variable to the fact that nullableFoo is not null when considering the if statement. In the second snippet, it is able to detect that because it's a direct null check on that variable, so smart casting can work.

[allan.conda]

I see. In actual nonNullFoo boolean has more conditions, but nullableFoo != null seems should be true 100% of the time.
Any tips how to handle this in code? It feels weird to have to do

if (nonNullFoo && nullableFoo != null)

again

[Vampire]

acceptsNonNullFoo(nullableFoo!!)

[allan.conda]

^ that bit me in the a$$ too quickly. I removed nonNullFoo and got a crash because I forgot about the !! 😄

[Adam S]

have you looked at contracts? https://www.baeldung.com/kotlin/contracts
You can write a custom 'validate not null' method, which the compiler will understand

@ExperimentalContracts
private fun validate(request: Request?) {
    contract {
        returns() implies (request != null)
    }
    if (request == null) {
        throw IllegalArgumentException("Undefined request")
    }
    if (request.arg.isBlank()) {
        throw IllegalArgumentException("No argument is provided")
    }
}

[dmitriy.novozhilov]

Such smartcasts will work in K2 compiler