Agreed about missing if and switch expressions in Swift. My preferred way of writing that would be:

    let foo: Int
    if x <= 0 {
        foo = 0
    } else if somethingElse > 50 {
        foo = 9000
    } else {
        foo = 42
    }

That way you get immutable foo and the compiler will shout at you if you forget to assign the value in one branch. It's not quite as nice as an expression, but it's less punctuation than the closure and the result is just as safe.