I'm having trouble getting this to work. There isn't too much information about this that I can find. I'm hoping maybe some smarter than me people on here could shed some light. The save function was taken from the only answer I could find from StackOverflow.

import AVFoundation
import Foundation

class Coordinator {

    let synthesizer: AVSpeechSynthesizer

    init() {
        let synthesizer = AVSpeechSynthesizer()
        self.synthesizer = synthesizer
    }

    func speakPhrase(phrase: String) {
        let utterance = AVSpeechUtterance(string: phrase)
        utterance.voice = AVSpeechSynthesisVoice(language: "en")
        synthesizer.speak(utterance)
    }

    func saveAVSpeechUtteranceToFile() {

        let utterance = AVSpeechUtterance(string: "test 123")
        utterance.voice = AVSpeechSynthesisVoice(language: "en")
        var output: AVAudioFile?

        synthesizer.write(utterance) { (buffer: AVAudioBuffer) in
            guard let pcmBuffer = buffer as? AVAudioPCMBuffer else {
                fatalError("unknown buffer type: \(buffer)")
            }
            if pcmBuffer.frameLength == 0 {
                // Done
            } else {
                // append buffer to file
                if output == nil {
                    output = try? AVAudioFile(
                        forWriting: URL(fileURLWithPath: "test.caf"),
                        settings: pcmBuffer.format.settings,
                        commonFormat: .pcmFormatInt16,
                        interleaved: false)
                }
                try! output?.write(from: pcmBuffer)
            }
        }
    }
}

import SwiftUI

struct ContentView: View {

    let coordinator = Coordinator()

    var body: some View {
        VStack {
            HStack {
                Image(systemName: "globe")
                    .imageScale(.large)
                    .foregroundColor(.accentColor)
                Text("Speak")
            }
            .padding()
            .onTapGesture() {
                coordinator.speakPhrase(phrase: "This works fine.")
            }
            HStack {
                Image(systemName: "globe")
                    .imageScale(.large)
                    .foregroundColor(.accentColor)
                Text("Save to File")
            }
            .padding()
            .onTapGesture() {
                coordinator.saveAVSpeechUtteranceToFile()
            }
        }
        .font(.largeTitle)
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}