通过 GuidedTour 学习 swift

Question

在 Swift 的 GuidedTour 示例中，作者是

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/

var optionalString: String? = "Hello"
optionalString == nil 
var optionalName: String? = "John Appleseed"    
var greeting = "Hello!"

if let name = optionalName {
    greeting = "Hello, \(   name)"
}

我不能做这个实验，因为错误

将 optionalName 更改为 nil。你得到什么问候？添加一个 else 子句，如果 optionalName 是 nil.

，则设置不同的问候语

Answer 1

当我创建新的 playground 并输入与您 post 完全相同的代码时，它起作用了。你能 post 完整的代码吗？

// Playground - noun: a place where people can play

import Foundation

var optionalString: String? = "Hello"
optionalString == nil
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
   greeting = "Hello, \(   name)"
}

唯一不同的是，您似乎忘记导入 Foundation 框架：

import Foundation

Answer 2

var optionalString: String? = "Hello"
print(optionalString == nil)



var optionalName: String? = nil
var greeting = "Hello!"
if let name = optionalName {
    greeting = "Hello, \(name)"
}else{
    greeting = "Hello Max"
}
greeting

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