Swift String Interpolation displaying optional?

Question

When i use the following code and have nameTextField be "Jeffrey" (or any other name)

@IBAction func helloWorldAction(nameTextField: UITextField) {

    nameLabel.text = "Hello, \(nameTextField.text)"

}

nameLabel displays... Hello, Optional("Jeffrey")

But, when I change the previous code to include a "!" like this:

@IBAction func helloWorldAction(nameTextField: UITextField) {

    nameLabel.text = "Hello, \(nameTextField.text!)"

}

The code works as expected and nameLabel displays.... Hello, Jeffrey

Why is the "!" required, in the video tutorial I used to create this simple program he did not use the "!" and the program worked as expected.

score 24 · Answer 1 · answered Dec 08 '15 at 15:13

24

Another alternative is to use the null coalescing operator within the interpolated string for prettier text without the need for if let.

nameLabel.text = "Hello, \(nameTextField.text ?? "")"

It's less readable in this case, but if there were a lot of strings it might be preferable.

answered Dec 08 '15 at 15:13

Craig McMahon

1,550
1
14
36

Whenever I use this it makes my build time quadruple. – Wayne Bloss Apr 01 '16 at 18:32
Unfortunately, in my case I'm trying to interpolate optional Int values -- can't coalesce with empty string. – RonLugge Mar 06 '17 at 06:50
@RonLugge No but you can with a zero :-) – Craig McMahon Mar 06 '17 at 07:05
1

@CraigMcMahon and a zero would be erroneous if you're building a path that may (or may not) have an object ID at the end. E. G. http://foo.bar/api/v1/foos/1/bars/(optional) – RonLugge Mar 06 '17 at 18:36

score 12 · Accepted Answer · answered Jul 14 '15 at 21:46

12

Optionals must be unwrapped. You must check for it or force unwrap as you do. Imagine the optional as a box where you put a value. Before you can access it, you need to put it out.

if let name = nameTextField.text {
    nameLabel.text = "Hello, \(name)"
}

answered Jul 14 '15 at 21:46

Tomáš Linhart

13,509
5
51
54

27

This seems like a terrible design choice by the creators of Swif for string interpolation. I don't know of any other language that does this. It makes way more sense to print the unwrapped value if it exists, otherwise print blank or nil. Or don't allow optionals inside of string interpolation. This has caused tons of bugs for us. – bobics Aug 26 '15 at 22:14

score 2 · Answer 3 · edited Mar 19 '19 at 09:40

2

Here's a handy extension to unwrap Any? to String.

Set a default value for nil values.

extension String {
    init(_ any: Any?) {
        self = any == nil ? "My Default Value" : "\(any!)"
    }
}

// Example

let count: Int? = 3
let index: Int? = nil
String(count)
String(index)

// Output
// 3
// My Default Value

edited Mar 19 '19 at 09:40

Mango

187
1
8

answered Jan 10 '19 at 08:06

Casper

152
12

Mikael Weiss · Answer 4 · 2020-08-08T17:53:16.203

You can also use optional map.
This is where I learned of how to use it.

Basically, map will take an optional and return a value if there's a value and return nil if there's no value. It think this makes more sense in code, so here's the code I found useful:

func getUserAge() -> Int? {  
    return 38  
}

let age = getUserAge()

let ageString = age.map { "Your age is \($0)" }
print(ageString ?? "We don't know your age.")

I guess this may not be super helpful in the case where you're passing in an optional string, (nil coalescing works just fine in that case), but this is super helpful for when you need to use some value that isn't a string.
It's even more useful when you want to run logic on the given value since map is a closure and you can use $0 multiple times.

Swift String Interpolation displaying optional?

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