iOS Tutorial Multi-Threading Basics: Image downloading in Swift 3 

Sure. :)

np man.

A Tic Tac Toe game with server side 2d can be easily realized using Firebase for free. Using Firebase, you can create a game room, you can think this process as a chatting precess, Firebase real database can let the user know once anything changed in that game room.

+Dina Moussa to define variable u can use this format name:Type. "!" Means it is an optional type.

Oh, Thank you!! I got confused because I know that NSURL is an objective C class but I didn't know that I can use it as a type of a variable... I thought I could just say: let url = NSURL ( string: urlStr)

+rahul bandal main thread is the only handles UI related events. Global is one of the background threads.