Swift：Nil与返回类型String不兼容 [英] Swift: Nil is incompatible with return type String

问题描述

我在Swift中有这个代码：

I have this code in Swift:

guard let user = username else{
        return nil
    }

但我收到以下错误：

Nil is incompatible with return type String

你知道为什么或如何在这种情况下返回nil？

Any of you knows why or how I return nil in this case?

我真的很感谢你的帮助

推荐答案

你必须告诉编译器你要返回nil。那你怎么样？通过在对象后面指定'？'。例如，看一下这段代码：

you have to tell the compiler that you want to return nil. How do you that? by assigning '?' after your object. For instance take a look at this code:

func newFriend(friendDictionary: [String : String]) -> Friend? {
    guard let name = friendDictionary["name"], let age = friendDictionary["age"] else {
        return nil
    }
    let address = friendDictionary["address"]
    return Friend(name: name, age: age, address: address)
}

请注意，我必须告诉编译器我的对象朋友我正在返回的是一个可选的'朋友？'，否则它会在我身上泄漏错误

Notice that i had to tell the compiler that my Object Friend that i'm returning is an optional 'Friend?' other wise it spill an error on me

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