Here's an example:

@OptIn(ExperimentalContracts::class)
fun myTest(foo: String?): String? {
    contract {
        returnsNotNull() implies (foo != null)
    }
    return foo
}

fun myFunction(foo: String?) {
    myTest(foo) ?: return

    foo.length // Error: requires safe or non-null asserted call

    if (myTest(foo) != null) {
        foo.length // No error
    }
}

In this snippet I have a dummy function

myTest

that which guarantees that if a non-null value is returned, the given parameter is also non-null. This should in theory mean that the first line of

myFunction

"guards" the

foo

value and that

foo

should be guaranteed to be non-null on all lines after that. Instead, this produces an error on the

foo.length

call, implying that no smart cast was possible. If we exlicitly perform this test in an if statement, however, the smart cast succeeds and the compiler seems to know that

foo

can no longer be null. Does anyone know if this is a limitation in how the compiler treats the

?: return

as opposed to an if statement? Or am I overlooking something? Thanks for the help!