《What’s New in Swift 5?》

Language Improvements

• 支持 isMultiple(of:)
• 使用##来显示反斜杠与“”
• 支持isNumber来判断字符是否为数字
• 支持isAlphabetic
• 去掉Subsequences

Dictionary

支持compactMapValues
DictionaryLiteral 改名为 KeyValuePairs

插入字符方法更新

swift4.2 组装string的步骤：将每个string包装成stringInterpolationSegment，再将所有stringInterpolationSegment包装成stringInterpolationSegment，形成新的string。

let language = "Swift"
let languageSegment = String(stringInterpolationSegment: language)
let space = " "
let spaceSegment = String(stringInterpolationSegment: space)
let version = 4.2
let versionSegment = String(stringInterpolationSegment: version)
let string = String(stringInterpolation: languageSegment, spaceSegment, versionSegment)

swift5
1.生成DefaultStringInterpolation
2.appendLiteral string

3. stringInterpolation 生成新的string

// 1
var interpolation = DefaultStringInterpolation(
  literalCapacity: 7,
  interpolationCount: 1)
// 2
let language = "Swift"
interpolation.appendLiteral(language)
let space = " "
interpolation.appendLiteral(space)
let version = 5
interpolation.appendInterpolation(version)
// 3
let string = String(stringInterpolation: interpolation)

将switch中的default 改名为@ unknown

新增 Result

Never 支持 Equatable 和 Hashable

增加dynamically callable types来与Python或Ruby等脚本语言互操作 dynamicallyCall

Package Manager更新

Platform Deployment Settings ，可指定minimum required platform deployment target version。如.iOS(.v12),
Target Build Settings，可定制化
Dependency Mirroring，新增
Making Codable Ranges，
Flattening Nested Optionals：try? in Swift 5 doesn’t create nested optionals
Removing Customization Points From Collections：移除了collection的Customization，因为容易产生理解错误。

• Identity Key Paths：Swift 4.2 通过 .self 来访问value

tutorial.self = Tutorial(title: "What's New in Swift 5?", author: "Cosmin Pupăză")

swift5 增加identity key paths。

tutorial[keyPath: \.self]= Tutorial(title: "What's New in Swift 5?", author: "Cosmin Pupăză")

• Build Configuration Updates
  增加 < ,可替代 !swift(>=5)

• Using Variadic Parameters for Enumeration Cases With Associated Values
  swift4.2 枚举值可以这样写 case tutorial(_: String...)
  swift5 中，不再支持，取代为case tutorial([String])

• Deprecating String Index Encoded Offsets
  swift 4.2 对string做UTF-16 编码。swift5则是UTF8.
  encodedOffset取代为 utf16Offset(in:)

总结

Swift 5 增加了ABI稳定，因此，今后的版本不会再有太大的改变。
更多内容可参考 CHANGELOG和Swift standard library diffs