Calling function with optional type in Swift

Question

Let's say I have the following:

var didConnectObserver: NSObjectProtocol?

didConnectObserver = NSNotificationCenter.defaultCenter().addObserverForName(
    MyKey, object: nil, queue: nil, usingBlock: { (note) -> Void in
    ...
})

At some point I unregister:

NSNotificationCenter.defaultCenter().removeObserver(didConnectObserver)

This doesn't work, though, because didConnectObserver is an optional. Is there a more compact way to write this than:

if let obs = didConnectObserver {
    NSNotificationCenter.defaultCenter().removeObserver(obs)
}

that still does the right thing if didConnectObserver is nil?

Answer 1

I'm still getting the hang of map with Optionals, but I believe this will work:

_ = didConnectObserver.map(NSNotificationCenter.defaultCenter().removeObserver)

If didConnectObserver is nil, the result of this is nil, otherwise it executes the function with didConnectObserver!. The _ = is necessary to suppress a warning Result of call to 'map' is unused.

Here's what autocomplete shows when you type didConnectObserver.map:

Here is another example of the same concept:

func add5(i: Int) {
    print("add 5 called")
    print(i + 5)
}

let a: Int? = 10

_ = a.map(add5)

If a is nil, then add5 is not called. If a is Optional(10), then add5 is called and 15 is printed.

It works just like:

if a != nil {
    add5(a!)
}