[ Swift ] synthesizer.speak 怎么出声？

#!/usr/bin/env swift
import AVFoundation
// Create an utterance.
let utterance = AVSpeechUtterance(string: "The quick brown fox jumped over the lazy dog.")

// Configure the utterance.
utterance.rate = 0.57
utterance.pitchMultiplier = 0.8
utterance.postUtteranceDelay = 0.2
utterance.volume = 0.8

// Retrieve the British English voice.
let voice = AVSpeechSynthesisVoice(language: "en-GB")

// Assign the voice to the utterance.
utterance.voice = voice
// Create a speech synthesizer.
let synthesizer = AVSpeechSynthesizer()

// Tell the synthesizer to speak the utterance.
synthesizer.speak(utterance)
synthesizer.speak(AVSpeechUtterance(string: "Hello The quick brown fox jumped over the lazy dog."))

var myString = "Hello, World!"
 
print(myString)

为啥这个没有声音，synthesizer 不能用 swsh 脚本使用？ 我是纯小白，也没学过 swift 今天发现 mac 的朗读功能挺有意思的就想调一下这个接口玩玩，但是发现没动静 感觉我的语法没问题啊，应该是 使用姿势不对吧，求指点要怎么用

目前就是想这个 出声音，求解