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I have a problem in swift 2.0

here is the current block of code that I write: 

let URL = NSURL(string:"www.google.com")

and then I get the following warning:"initialization of immutable value URL was never used, consider replacing with assignment to '_' or removing it.

What should i do when I want to declare a let.

I get a similar warning when writing var URL = NSURL(string: "www.google.com")

What can I do in swift 2.0 to declare a Let or a var?

Midhun MP
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Jonathan Meguira
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    I think you are not using that `URL` object anywhere in your code, that's why swift throwing that warning. Actually I'm not seeing that warning with URL object, instead seeing that warning for data object !!! (From the screenshot) – Midhun MP Nov 23 '15 at 09:11
  • If you are not using variable `data`, don't declare it. – Sulthan Nov 23 '15 at 09:14
  • You are not using `data` because you declare it but then it is re-declared as a parameter in the callback and that's what you're actually using. – Wain Nov 23 '15 at 09:15
  • Here is my current code: { let URL = NSURL(string: "www.amazon.com") let data = NSURLSession.sharedSession().dataTaskWithURL(URL!) { (data, response, error) in if (error == nil){ let urlContent = NSString(data: data!, encoding: NSUTF8StringEncoding) print(urlContent) } } } and i still get the same error even though i replaced var with let – Jonathan Meguira Nov 23 '15 at 09:17

4 Answers4

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initialization of immutable value URL was never used

Means that you didn't use the variable anywhere, so its throwing a warning. But looking at the screenshot, you have declared URL as a var and used it in data which is another var.

So there should be two warnings now. URL is declared as a var but never mutated and data variable was never used.

To satisfy, use let URL ... since you are not mutating it. and do away with data as this is a async block/closure and you can access data from the completion block.

Note:

You should use let when you are not modifying it later and you should use var when you want to modify the object. Consider array :

let immutableArray:[String] = ["foo", "bar"]
var mutableArray:[String] = ["hello"]

mutableArray.append("World") // Is valid since its a var
immutableArray.append("abc") // Not valid, infact auto complete does not even show append methods
Eric Aya
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GoodSp33d
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Whenever you are declaring a let and not using that constant complier will show a warning. There is nothing to worry about. If you are not using let constant replace it with _. It is for optimization. If you are not using remove that let. Or to silence warning use a simple print(YOUR Constant) For your case user 

let url = URL = NSURL(string:"www.google.com")

Than

let data = NSURLSession.sharedSession().downloadTaskWithURL(URL!) {
{ (data, response, error) in {
  if(error != nil) {
  print(data) // This data is different from let data constant
}
print(data) // This will silence warning. Also make sure it is not nil
Saqib Omer
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this may work fine.

let URL = NSURL(string:"www.google.com")
NSURLSession.sharedSession().downloadTaskWithURL(URL!) { (url: NSURL?, response: NSURLResponse?, error: NSError?) -> Void in
    if error == nil && url != nil {
        let data = NSData(contentsOfURL: url!)
            print(data)
        }
    }
Kingiol
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You should change var to let to resolve this warning. To save memory, Compiler recommend user to use let instead of var when you only need to get value from a variable but not set

khoiNN
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