Swift: Testing optionals for nil

Question

I\'m using Xcode 6 Beta 4. I have this weird situation where I cannot figure out how to appropriately test for optionals.

If I have an optional xyz, is the correct w

Answer 1

To add to the other answers, instead of assigning to a differently named variable inside of an if condition:

var a: Int? = 5

if let b = a {
   // do something
}

you can reuse the same variable name like this:

var a: Int? = 5

if let a = a {
    // do something
}

This might help you avoid running out of creative variable names...

This takes advantage of variable shadowing that is supported in Swift.

Answer 2

If you have conditional and would like to unwrap and compare, how about taking advantage of the short-circuit evaluation of compound boolean expression as in

if xyz != nil && xyz! == "some non-nil value" {

}

Granted, this is not as readable as some of the other suggested posts, but gets the job done and somewhat succinct than the other suggested solutions.

Answer 3

Also you can use Nil-Coalescing Operator

The nil-coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that is stored inside a.

let value = optionalValue ?? defaultValue

If optionalValue is nil, it automatically assigns value to defaultValue

Answer 4

Instead of if, ternary operator might come handy when you want to get a value based on whether something is nil:

func f(x: String?) -> String {
    return x == nil ? "empty" : "non-empty"
}

Answer 5

var xyz : NSDictionary?

// case 1:
xyz = ["1":"one"]
// case 2: (empty dictionary)
xyz = NSDictionary() 
// case 3: do nothing

if xyz { NSLog("xyz is not nil.") }
else   { NSLog("xyz is nil.")     }

This test worked as expected in all cases. BTW, you do not need the brackets ().

Answer 6

Another approach besides using if or guard statements to do the optional binding is to extend Optional with:

extension Optional {

    func ifValue(_ valueHandler: (Wrapped) -> Void) {
        switch self {
        case .some(let wrapped): valueHandler(wrapped)
        default: break
        }
    }

}

ifValue receives a closure and calls it with the value as an argument when the optional is not nil. It is used this way:

var helloString: String? = "Hello, World!"

helloString.ifValue {
    print($0) // prints "Hello, World!"
}

helloString = nil

helloString.ifValue {
    print($0) // This code never runs
}

You should probably use an if or guard however as those are the most conventional (thus familiar) approaches used by Swift programmers.