Recently while doing some migration from objective-c to swift and I found a line of code that seemed to me that it should crash, and yet, it didn’t crash on production. It was an objective-c code bridged to swift as an implicit unwrapped (!). So here is the snippet, more or less:

// The bridged generated interface from the objective-c
class BridgedClass {
    var importantNote: String! // contains a nil value
}

// ... then I had a function:

func doSomething(importantNote: String?) {
    print(note)
}

// ... and it was called

doSomething(importantNote: myBridgedInstance.importantNote) // Should it crash?

The answer as you may already know is IT DOESN’T CRASH!, but why? Isn’t myBridgedInstance.importantNote accessing a nil value? Why it is printing nil?

So to understand that I went to a swift playground and in short what is happening underhood is:

doSomething(importantNote: myBridgedInstance.importantNote)
// this is same as:
let importantNote: String? = Optional(myBridgedInstance.importantNote)
print(importantNote)

And therefore it won’t crash, as it is now an Optional. Crazy huh? However if by any chance the developer had changed the signature of the method to:

func doSomething(importantNote: String)

Then it would crash on his face!

Music

A bit of this and that… old times