CODEWITHSUNDEEP
iosswiftswift2let
Jonathan Meguira
Jonathan Meguira

Reputation: 1969

Swift 2.0 and let warnings

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?

Upvotes: 0

Views: 587

Answers (4)

khoiNN
khoiNN

Reputation: 45

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

Upvotes: 0

GoodSp33d
GoodSp33d

Reputation: 6282

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

Upvotes: 4

Kingiol
Kingiol

Reputation: 1145

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)
        }
    }

Upvotes: 0

Saqib Omer
Saqib Omer

Reputation: 5477

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

Upvotes: 0

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