在声明字符串类型时为其赋值，在 swift 中使用 if-else 控制流

Question

我正在通过 swift文档学习 Swift 。在学习控制流语句时，在 if-else 部分语句中，我使用了文档中给出的这段代码，但它给出了一个错误，指出此语法是错误的。

let temperatureInCelsius = 25

let weatherAdvice = if temperatureInCelsius <= 0 {
    "It's very cold. Consider wearing a scarf."
} else if temperatureInCelsius >= 30 {
    "It's really warm. Don't forget to wear sunscreen."
} else {
    "It's not that cold. Wear a T-shirt."
}
print(weatherAdvice)

错误：

在此代码之后的文档中，又给出了一个代码，该代码给出了相同的错误，再加上一个错误“nil”需要上下文类型”

let weatherAdvice = if temperatureInCelsius <= 0 {
    "It's very cold. Consider wearing a scarf."
} else if temperatureInCelsius >= 30 {
    "It's really warm. Don't forget to wear sunscreen."
} else {
    "It's not that cold. Wear a T-shirt."
}


print(weatherAdvice)

Answer 1

这是Swift 5.9 的一项功能，您需要在 Xcode 14 或 Xcode 15 beta 中安装最新的 Swift 5.9 工具链。

否则按照传统方式进行

let temperatureInCelsius = 25
let weatherAdvice: String

if temperatureInCelsius <= 0 {
    weatherAdvice = "It's very cold. Consider wearing a scarf."
} else if temperatureInCelsius >= 30 {
    weatherAdvice = "It's really warm. Don't forget to wear sunscreen."
} else {
    weatherAdvice = "It's not that cold. Wear a T-shirt."
}


print(weatherAdvice)
// Prints "It's not that cold. Wear a T-shirt."