Error converting Obj-C function completion handler code to Swift 2.0

Question

I'm having trouble converting / understanding how Obj-C completion handlers work, and how I can convert them to Swift 2.0... Specifically, here is the code:

[BLAH aRandomTaskWithURL:NSURL completion:^(NSURL *compVar) {

//do something with compVar

}];

here is my attempt:

BLAH.aRandomTaskWithURL(myURL,completion: (compVar:NSURL)  ) {

            print(compVar)
   }

the above produces the error "delete compVar:" ... so i delete it, and then it says "cannot invoke type (NSURL) with argument list of type ' ( () -> () )'

I've tryed several times to define the Swift 2.0 equiv of compVar, but to no luck... I've also read ( and followed along with ) the relevant documentation on Swift completion variables, again to no luck. What am I missing?

But, when I add "Void in"

BLAH.aRandomTaskWithURL(myURL, completion:  ) { Void in

            //do something
    }

there is no error, but I don't have access to what should be the completion variable.

here is the actual obj-c code ( i was just trying to keep it general before ):

(void)optimalGIFfromURL:(NSURL*)videoURL loopCount:(int)loopCount completion:(void(^)(NSURL *GifURL))completionBlock {

Answer 1

It is either:

BLAH.aRandomTaskWithURL(myURL, completion: { compVar: NSURL in
    print(compVar)
})

Or, using trailing closure syntax:

BLAH.aRandomTaskWithURL(myURL) { compVar: NSURL in
    print(compVar)
}

---

FYI, it also depends upon the nullability configuration of the NSURL parameter. If nullability hasn't been specified, it would be:

BLAH.aRandomTaskWithURL(myURL) { compVar: NSURL! in
    print(compVar)
}

Or, if it was explicitly marked as nullable:

BLAH.aRandomTaskWithURL(myURL) { compVar: NSURL? in
    print(compVar)
}

Or, easiest, you can just have the compiler infer the nullability:

BLAH.aRandomTaskWithURL(myURL) { compVar in
    print(compVar)
}

If you've properly imported the headers for aRandomTaskWithURL, code completion will show you the correct configuration of the compVar (whether optional or not).