Swift 2 - “if"中的模式匹配 [英] Swift 2 - Pattern matching in "if"

问题描述

最近我看到了 Apple 的 WWDC 2015 主题演讲.我还查看了一些文档，但我找不到if 中的模式匹配"部分，它是如何写在他们展示的其中一张幻灯片上的.(来自 Apple Events 的 68 分 00 秒视频)

Recently I've saw the WWDC 2015 keynote from Apple. I also looked at some documentation but I can't find a "pattern matching in if" section, how it was written on one of the slides which they have shown. (68min 00sec video from Apple Events)

你知道这是什么意思吗?还是语法?

Do you know what's this refers to? Or the syntax?

推荐答案

它真正的意思是 if 语句现在支持模式匹配，就像 switch 语句已经拥有的那样.例如，以下是使用 if/else if/else 语句切换"枚举案例的有效方法.

All it really means is that if statements now support pattern matching like switch statements already have. For example, the following is now a valid way of using if/else if/else statements to "switch" over the cases of an enum.

enum TestEnum {
    case One
    case Two
    case Three
}

let state = TestEnum.Three

if case .One = state {
    print("1")
} else if case .Two = state {
    print("2")
} else {
    print("3")
}

以下是检查 someInteger 是否在给定范围内的可接受方法.

And the following is now an acceptable way of checking if someInteger is within a given range.

let someInteger = 42
if case 0...100 = someInteger {
    // ...
}

这里有几个使用来自 The Swift Programming Language

Here are a couple more examples using the optional pattern from The Swift Programming Language

let someOptional: Int? = 42
// Match using an enumeration case pattern
if case .Some(let x) = someOptional {
    print(x)
}

// Match using an optional pattern
if case let x? = someOptional {
    print(x)
}

这篇关于Swift 2 - “if"中的模式匹配的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！