斯威夫特:守卫让与如果让 [英] Swift: guard let vs if let

问题描述

我一直在阅读有关 Swift 中的 Optionals 的内容，并且我看到了一些示例，其中 if let 用于检查 Optional 是否包含一个值，如果确实如此 - 对解包的值执行一些操作.

I have been reading about Optionals in Swift, and I have seen examples where if let is used to check if an Optional holds a value, and in case it does – do something with the unwrapped value.

然而，我已经看到在 Swift 2.0 中，关键字 guard let 被主要使用.我想知道 if let 是否已从 Swift 2.0 中删除，或者是否仍然可以使用.

However, I have seen that in Swift 2.0 the keyword guard let is used mostly. I wonder whether if let has been removed from Swift 2.0 or if it still possible to be used.

我应该将包含 if let 的程序更改为 guard let 吗?

Should I change my programs that contain if let to guard let?

推荐答案

if let 和 guard let 服务类似但不同的目的.

if let and guard let serve similar, but distinct purposes.

guard 的else"情况必须退出当前作用域.通常这意味着它必须调用 return 或中止程序.guard 用于提供提前返回，而无需嵌套函数的其余部分.

The "else" case of guard must exit the current scope. Generally that means it must call return or abort the program. guard is used to provide early return without requiring nesting of the rest of the function.

if let 嵌套了它的作用域，不需要任何特殊的东西.它可以返回，也可以不返回.

if let nests its scope, and does not require anything special of it. It can return or not.

一般来说，如果 if-let 块将成为函数的其余部分，或者它的 else 子句将有一个 return 或在其中中止，那么您应该使用 guard 代替.这通常意味着(至少根据我的经验)，当有疑问时，guard 通常是更好的答案.但是在很多情况下 if let 仍然是合适的.

In general, if the if-let block was going to be the rest of the function, or its else clause would have a return or abort in it, then you should be using guard instead. This often means (at least in my experience), when in doubt, guard is usually the better answer. But there are plenty of situations where if let still is appropriate.

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