在Swift中使用if in赋值的用法 [英] Usage of where in if let assignment in Swift

问题描述

Swift手册第61页的Swift文档提示可以使用 where 来加入具有常规条件的可选绑定。然而，当我这样做时，我有一个警告，建议我用以下代码中的逗号替换 where ：

The Swift documentation at page 61 of the Swift manual hints to the possibility of using where to join an optional binding with a regular condition. Yet when I do it I have a warning suggesting me to substitute the where with a comma like in the following piece of code:

if let geocodingError = error as? NSError where geocodingError.code == 2

推荐答案

在Swift 3中这个语法已经改变了。

In Swift 3 this syntax has changed.

什么是

如果让x = y，a = b其中a = = x {

现在

如果让x = y，设a = b，a == x {

理由是<$ c $的每个子条款c> if ... {现在是一个独立的布尔测试。

The justification is that each sub-clause of the if ... { is now an independent boolean test.

参见Xcode 发行说明& Swift Evolution提案了解更多相关信息改变。

See the Xcode Release notes & the Swift Evolution proposal for more info about this change.

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