ObjC to Swift : [NSOperationQueue addOperationWithBlock:]

Objective-C (main queue)

[[NSOperationQueue mainQueue] addOperationWithBlock:
^{
    //  do some UI stuff
}];

Objective-C (background queue)

NSOperationQueue * backgroundQueue = [[NSOperationQueue alloc] init];

[backgroundQueue addOperationWithBlock:
^{
    //  do some heavy stuff in background
}];

Swift (main queue)

NSOperationQueue.mainQueue().addOperationWithBlock
{() -> Void in

    //  do some UI stuff
}

Swift (background queue)

let backgroundQueue = NSOperationQueue()

backgroundQueue.addOperationWithBlock
{() -> Void in

    //  do some heavy stuff in background
}