Bound value in a conditional binding must be of Optional Type

Question

I have a protocol defined:

protocol Usable {
    func use()
}

and a class that conforms to that protocol

class Thing: Usabl         


        

Answer 1

As metioned in the Swift doc, the is operator is the guy you need for the job:

The is operator checks at runtime to see whether the expression is of the specified type. If so, it returns true; otherwise, it returns false.

The check must not be known to be true or false at compile time.

Therefore, the following test would normally be what you need:

if thing is Usable { 
    usableThing.use()
} else {
    println("can't use that")
}

However, as the doc specifies, Swift can detect at compile time that the expression is always true and declares an error to help the developer.