三个协议

RawRepresentable协议

public protocol RawRepresentable {
associatedtype RawValue
init?(rawValue: Self.RawValue)
varrawValue: Self.RawValue {get}
}
/// The `RawRepresentable` protocol is seen mainly in two categories of types: enumerations with raw value types and option sets.1、 For any enumeration with a string, integer, or floating-point raw type, the Swift compiler automatically adds `RawRepresentable` conformance. 
/// enum Counter: Int {
/// case one = 1, two, three, four, five
/// }
/// 2、 Option sets all conform to `RawRepresentable` by inheritance using the `OptionSet` protocol.
// 单独使用 RawRepresentable 的情况

struct Goods: RawRepresentable {
  // 使用非可选初始化方法实现协议可选的初始化方法要求
  init(rawValue: Int) {
    self = Goods()
  }
  var rawValue: Int
  typealias RawValue = Int
  init() {
    self.rawValue = 0
  }
}

SetAlgebra协议

publicprotocolSetAlgebra : Equatable, ExpressibleByArrayLiteral {
/// A type for which the conforming type provides a containment test.
/// associatedtypeElement
init()
funccontains(_member: Self.Element) -> Bool
funcunion(_other: Self) -> Self
funcintersection(_other: Self) -> Self
funcsymmetricDifference(_other: Self) -> Self
mutatingfuncinsert(_newMember: Self.Element) -> (inserted: Bool, memberAfterInsert: Self.Element)
mutatingfuncremove(_member: Self.Element) -> Self.Element?
mutatingfuncupdate(with newMember: Self.Element) -> Self.Element?
mutatingfuncformUnion(_other: Self)
mutatingfuncformIntersection(_other: Self)
mutatingfuncformSymmetricDifference(_other: Self)
    ......

OptionSet协议

publicprotocolOptionSet : RawRepresentable, SetAlgebra {
associatedtypeElement = Self
init(rawValue: Self.RawValue)
}

// OptionSet等价写法

publicprotocolOptionSet : SetAlgebra {
associatedtypeElement = Self
init(rawValue: Self.RawValue)
  associatedtypeRawValue
//init?(rawValue: Self.RawValue) // 非可选初始化方法可涵盖此方法
varrawValue: Self.RawValue {get}
}

OptionSet 定义类型

以结构体类型为例，MusicSets 如下：

structMusicSets: OptionSet {
//typealiasElement = Self
typealiasRawValue = Int
varrawValue: Int
init(rawValue: Int) {
self.rawValue = rawValue
  }
}

// 注意： MusicSets 对 SetAlgebra协议的实现 默认由OptionSet Extension，见下文“OptionSet 的 Extension分析”
// 简化版
structMusicSets: OptionSet {
varrawValue: Int
// 编译器自动推导
//  typealias RawValue = Int
init(rawValue: Int) {
self.rawValue = rawValue
  }
}

// 精简版
structMusicSets: OptionSet {
varrawValue: Int
// 编译器自动推导
//  typealias RawValue = Int
// 编译器自动生成（包含所有需要初始化的 成员变量, rawValue）
//  init(rawValue: Int) {
//    self.rawValue = rawValue
//  }
}

// 或者
structMusicSets: OptionSet {
//  var rawValue: Int
letrawValue: Int
}

加上类属性，如下是一个通常的OptionSet写法

structMusicSets: OptionSet {
//  var rawValue: Int
letrawValue: Int
  // 0001
  // 0010
  // 0100
  // 1000
  // 0111
staticletclassic = MusicSets(rawValue: 1 << 0)
staticletcountry = MusicSets(rawValue: 1 << 1)
staticletrock = MusicSets(rawValue: 1 << 2)
staticletpop = MusicSets(rawValue: 1 << 3)
staticletmix = MusicSets(rawValue: 7)
}

OptionSet 使用

OptionSet 在Swift当中 填补了Enum中缺少的 bitmask 位选集合的功能

functest() {
  let sets1 = MusicSets.classic
  let sets2 = MusicSets.country
  let sets3 = MusicSets.rock
  let sets4 = MusicSets.pop
  let music = MusicSets.mix
  print("Mix contains1: ", music.contains(sets1))
  print("Mix contains2: ", music.contains(sets2))
  print("Mix contains3: ", music.contains(sets3))
  print("Mix contains4: ", music.contains(sets4))

  let music2: MusicSets = [sets1, sets2, sets3]
  print("Set contains1: ", music2.contains(sets1))
  print("Set contains2: ", music2.contains(sets2))
  print("Set contains3: ", music2.contains(sets3))
  print("Set contains4: ", music2.contains(sets4))
  print("Set rawValue: ", music2.rawValue)
  }

OptionSet 的 Extension 分析

OptionSet 的 rawValue？ 可以 定义String类型吗？

Error: Type 'MusicSets2' does not conform to protocol 'SetAlgebra'
structMusicSets2: OptionSet {
    //    var rawValue: Int
letrawValue: String
//    init?(rawValue: String) {
//        <#code#>
//    }

//    init() {
//        <#code#>
//    }

//    mutating func formUnion(_ other: __owned MusicSets) {
//        <#code#>
//    }

//    mutating func formIntersection(_ other: MusicSets) {
//        <#code#>
//    }

//    mutating func formSymmetricDifference(_ other: __owned MusicSets) {
//        <#code#>
//    }
}

rawValue 改成 String 之后，就出现编译错误：类型'MusicSets2' 未遵守 SetAlgebra协议，很有可能一些默认的实现被磨掉了。下面从 OptionSet 的扩展中去查找答案(optionSet 有若干个扩展，默认实现了很多功能，详情请参考官网文档)。

Extension: 1 通用实现

/// `OptionSet` requirements for which default implementations
/// are supplied.
extensionOptionSet {
@inlinablepublicfuncunion(_other: Self) -> Self
@inlinablepublicfuncintersection(_other: Self) -> Self
@inlinablepublicfuncsymmetricDifference(_other: Self) -> Self
}

Extension: 2 Where 条件实现

/// `OptionSet` requirements for which default implementations are
/// supplied when `Element == Self`, which is the default.
extensionOptionSetwhereSelf == Self.Element {
@inlinablepublicfunccontains(_member: Self) -> Bool
@inlinablepublicmutatingfuncinsert(_newMember: Self.Element) -> (inserted: Bool, memberAfterInsert: Self.Element)
@inlinablepublicmutatingfuncremove(_member: Self.Element) -> Self.Element?
@inlinablepublicmutatingfuncupdate(with newMember: Self.Element) -> Self.Element?
}

Extension: 3 Where 条件实现

extensionOptionSetwhereSelf.RawValue : FixedWidthInteger {
@inlinablepublicinit()
@inlinablepublicmutatingfuncformUnion(_other: Self)
@inlinablepublicmutatingfuncformIntersection(_other: Self)
@inlinablepublicmutatingfuncformSymmetricDifference(_other: Self)
}

补充：协议的关联类型测试

protocolProtocol0 {
  // 关联类型 没有约束、有默认值
associatedtypeElement0 =Self
}
protocolProtocol1 {
  // 关联类型有约束
associatedtypeElement1: UIView
}
protocolProtocol2 {
  // 关联类型 没有约束、有默认值
associatedtypeElement2 = UIView
}
protocolProtocol3 {
  // 关联类型有约束、有默认值
associatedtypeElement3: UIView = UIButton
}
protocolProtocol04 {
  // 关联类型有约束
associatedtypeElement041: UIView
associatedtypeElement042: UIView
}
protocolProtocol4: Protocol04 {
  // 关联类型有约束、有默认值
associatedtypeElement041 = UIResponder
associatedtypeElement042 = UIButton
associatedtypeElement4: UIView = UIButton
}

structMusic: Protocol0, Protocol1, Protocol2, Protocol3, Protocol4 {
  // 必须指定类型
typealiasElement1 = UIButton
  // 有默认值，可以不指定类型，也可以改变指向
typealiasElement0 = NSObject
typealiasElement2 = NSObject
//  typealias Element3 = NSObject
typealiasElement3 = UIButton
typealiasElement4 = UIButton
  // Element041 有: UIView约束，因此 Protocol4中 对 Element041 的指定（成为Music的默认指定）不符合约束要求，需要重新指定
typealiasElement041 = UIButton
}