1

Xcode let's me use this initializer in my iOS 13.4 targeted project:

String(init(unsafeUninitializedCapacity:initializingUTF8With:)

But when I open my macOS 10.15 targeted package, the function is simply is not recognized by Xcode. As if it did not exist. I have the same problem from the command line:

> swift --version        
Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1)
Target: x86_64-apple-darwin19.6.0
> swift package --version
Swift Package Manager - Swift 5.3.0
> swift build
...
6:21: error: extraneous argument label 'unsafeUninitializedCapacity:' in call
  let cafe1 = String(unsafeUninitializedCapacity: validUTF8.count) {

Here is part of Package.swift:

// swift-tools-version:5.3
import PackageDescription
let package = Package(
  name: "abc",
  platforms: [.macOS(.v10_15)],
  products: [

I am running Xcode 12.0.1 (12A7300), 12.Catalina 10.15.7
Do I need a newer version of the Swift package manager? Any other ideas?

2

Initializers can be called in two ways in Swift: in this case you can initialize a String either with

let str = String(unsafeUninitializedCapacity: ..., initializingUTF8With: ...)

or by using .init on the type explicitly

let str = String.init(unsafeUninitializedCapacity: ..., initializingUTF8With: ...)

You can find some examples of that particular initializer in the appropriate documentation page.

3

I get that - but it has nothing to do with my question. What I used was the example in the documentation. Works for my IOS project, not for my macOS project.

4

My bad. If you cmd + click on the initializer and then click on Jump to Definition you will see:

@available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *)
public init(unsafeUninitializedCapacity capacity: Int, initializingUTF8With initializer: (UnsafeMutableBufferPointer<UInt8>) throws -> Int) rethrows

so, that initializer is only available on macOS 11.0 (Big Sur). It's also marked as available on iOS 14, are you sure you run your app on iOS 13.4?

1 Like
5

Thanks, great answer. Maybe I'll download macOS 11.0 Beta. Any idea when macOS 11 will be released?

6

Before the end of 2020, at worst.

7

You're right it's iOS14.

8

Big Sur 11 should be released in this month.

9

I'm new to swift and installed xcode, followed the hello tutorial, and got the same message you did. So, after reading this, I updated to the beta, and I am still getting that error.

10

What version of MacOS/iOS are developing on? What version of MacOS/iOS are you deploying to? Deployment target has to be MacOS 11.0 (has not been released yet) for macOS, iOS14 for iOS, similar for iPAD OS.