🅿️OptionSet

• 如果變數的行為像「單選題」，可考慮用 enum。

• 如果類似「多選題」，可考慮用 OptionSet。

⭐️ 使用

When creating an option set, include a rawValue property in your type declaration. For your type to automatically receive default implementations for set-related operations, the rawValueproperty must be of a type that conforms to the FixedWidthInteger protocol, such as Intor UInt8.

struct ShippingOptions: OptionSet {
    // ⭐️ required property
    let rawValue: Int    // ⭐️ conforms to 🅿️ FixedWidthInteger
}

Next, create unique options as static properties of your custom type using unique powers of two (1, 2, 4, 8, 16 ...) for each individual property’s raw value so that each property can be represented by a single bit of the type’s raw value.

struct ShippingOptions: OptionSet {

    let rawValue: Int

    // ⭐️ unit sets (containing only one element)
    static let nextDay    = ShippingOptions(rawValue: 1 << 0)
    static let secondDay  = ShippingOptions(rawValue: 1 << 1)
    static let priority   = ShippingOptions(rawValue: 1 << 2)
    static let standard   = ShippingOptions(rawValue: 1 << 3)

    // ⭐️ useful sets (containing multiple elements)
    // ⭐️ can be initialized by array literal (ExpressibleByArrayLiteral)
    static let express: ShippingOptions = [.nextDay, .secondDay]
    static let all: ShippingOptions = [.express, .priority, .standard]
}

// ⭐️ empty set
let noOptions: ShippingOptions = []

⭐️ 注意：OptionSet 的 methods 雖然看起來像是元素與集合間的用語 (源自於 SetAlgebra)，但要注意每個 OptionSet 的 static properties 本質上還是一個「集合」的概念，就算只包含一個元素都是如此！

var A: ShippingOptions = []
let B: ShippingOptions = .priority

// ⭐️ 雖然以下是集合與元素間的用語，但 A 跟 B 其實都是集合喔！
A.insert(B)
A.contains(B)

💈範例

• DimensionPositions - used by .dimension() to decorate views.

• Logger - Logger.TableOptions is an OptionSet.

Other examples:

let price = 87
var options: ShippingOptions = []

if price > 50 { options.insert(.priority) }
if options.contains(.priority) { ... } 

📜 協定

📗 參考

• How to solve problems with bitwise operators in Swift - Natascha Fadeeva
• Singleton (mathematics) - Wikipedia
• Understanding Swift’s OptionSet - Donny Wals
• OptionSet - NSHipster
• Swift, more elegant code: OptionSet - Ahmad Fayyas

📘 手冊

• Swift ⟩ Standard Libary ⟩ Collections ⟩

  • OptionSet
  • SetAlgebra

👥 相關

• .dimension() - use OptionSet to help decorate views.