Swift String format vs Objective-C

Question

I am using swift String(format:...) and need to compute values in the format string itself using ternary operator, something like this but it doesn't compiles.

 String(format: "Audio: \(numChannels>1?"Stereo": "Mono")")

In Objective-C, I could do like this:

 [NSString stringWithFormat:@"Audio: %@",  numChannels > 1 ? @"Stereo" : @"Mono"];

How do I achieve the same elegance in Swift without having an intermediate variable?

Note that your Objective-C version does not compute the values in the format string itself. The format is fixed and the argument computes the string. — Martin R
– Martin R, Commented Aug 12, 2018 at 9:31
@MartinR That's correct, but in Swift I could compute values, such as '\(sampleRate/1000)' in format string itself. — Deepak Sharma
– Deepak Sharma, Commented Aug 12, 2018 at 9:32
Perhaps you mean string interpolation: let s = "Audio: \(numChannels > 1 ? "Stereo" : "Mono")" — Martin R
– Martin R, Commented Aug 12, 2018 at 9:33
The reason that your Swift code does not compile is the missing spaces around ? and : — Martin R
– Martin R, Commented Aug 12, 2018 at 9:35
You can even compose the string without String(format and without String Interpolation: "Audio :" + (numChannels > 1 ? "Stereo" : "Mono") — vadian
– vadian, Commented Aug 12, 2018 at 11:47

Martin R · Accepted Answer · 2018-08-12 09:43:36Z

2

Due to the missing spaces around the operators in the conditional expression, the compiler misinterprets 1?"Stereo" as optional chaining. It should be

String(format: "Audio: \(numChannels>1 ? "Stereo" : "Mono")")

instead. However, since the format string has no placeholders at all, this is equivalent to

"Audio: \(numChannels > 1 ? "Stereo" : "Mono")"

answered Aug 12, 2018 at 9:43

Martin R

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Comments

Joakim Danielson · Accepted Answer · 2018-08-12 20:17:41Z

1

One option is to use String(format:) with a placeholder and the conditional expression as the parameter for the placeholder

String(format: "Audio = %@", numChannels > 1 ? "Stereo" : "Mono")

edited Aug 12, 2018 at 20:17

answered Aug 12, 2018 at 9:29

Joakim Danielson

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6 Comments

Martin R Over a year ago

It should be %@ for a Swift string.

Joakim Danielson Over a year ago

Yeah, I realised that

vacawama Over a year ago

@DeepakSharma, the %@ legacy from Objective-C is because String(format:) is not pure Swift but comes by way of the Foundation framework. Note that you have to import Foundation (or UIKit or AppKit or Cocoa) to use it. So "Stereo" and "Mono" get passed as NSString.

Joakim Danielson Over a year ago

Why was this downvoted? It works as expected and is one of several valid solutions.

Ashley Mills Over a year ago

Code only answers are improved with some explanation

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