Variable/constant declaration difference

Question

Which of those is best and is any of these declarations per se redundant?

let imageView: UIImageView = UIImageView() // [1]
let imageView = UIImageView()              // [2]
let imageView: UIImageView!                // [3]
let imageView: UIImageView?                // [4]

Did you check if all your options compile? And what is the aim you're trying to achieve? — Wain, Sep 12 '15 at 23:35
@Wain I'm using [1] and it compiles perfectly. Should I try another one or leave it ? is there a difference between [1] and [2] ? — leyke077, Sep 12 '15 at 23:40
@leyke077 There is no difference except for readability. The second one is better — Leo Dabus, Sep 12 '15 at 23:47
[3] and [4] just declare optionals that haven't been initialized yet. — vacawama, Sep 12 '15 at 23:49

R Menke · Accepted Answer · 2015-10-09T02:36:31.887

Added some comments too your examples.

two ways to init
two ways to declare an optional
I also added the late init option

Google optionals for more info.

// more text for more readability
let imageViewA: UIImageView = UIImageView() // [1]

// this is fine
let imageViewB = UIImageView()              // [2]

// this is danagerous
let imageViewC: UIImageView!                // [3]

// calling this before the next step will crash it
imageViewC.image = UIImage(data: NSData())

// it needs this step
imageViewC = UIImageView()

// this is fine because xcode will warn you when you are not handling it fine
let imageViewD: UIImageView?                // [4]

// it does needs this step
imageViewD = UIImageView()

// late init : this is cool stuff
let imageViewE: UIImageView

imageViewE = UIImageView()

Variable/constant declaration difference

1 Answers1