如何使用swift playground将概率分配给switch语句中的随机间隔？

import PlaygroundSupport
import GameplayKit

let randomSource = GKRandomSource.sharedRandom()

let probabilities = [0.2, 0.3, 0.5]

let distribution = GKShuffledDistribution(randomSource: randomSource, lowestValue: 0, highestValue: probabilities.count - 1, probabilities: probabilities)

switch distribution.nextInt() {
case 0:
    // 执行第一个间隔的代码
case 1:
    // 执行第二个间隔的代码
case 2:
    // 执行第三个间隔的代码
default:
    break
}