分配可變參數的參數變量

Question

這個名單是這樣的：

public enum NodeFeature: UInt16 { 
    case relay  = 0x01 
    case proxy  = 0x02 
    case friend  = 0x04 
    case lpn  = 0x08 
} 

public struct NodeFeatures { 
    public let rawValue: UInt16 

    public init(rawValue: UInt16) { 
     self.rawValue = rawValue 
    } 

    public init(features: NodeFeature...) { 
     var rawValue = UInt16(0) 
     for feature in features { 
      rawValue |= feature.rawValue 
     } 
     self.rawValue = rawValue 
    } 

    public func hasFeature(_ feature: NodeFeature) -> Bool { 
     return rawValue & feature.rawValue > 0 
    } 
} 

這是從服務器的響應：

"feature": { 
    "relay": true, 
    "proxy": false, 
    "friend": false, 
    "lowPower": false 
} 

現在我需要創建的NodeFeatures只有true值的實例：

var features = [NodeFeature]() // how to declare and prepare the list of args? 

if true { 
    features.append(.first) 
} else if true { 
    features.append(.third) 
} 

let wrapper = NodeFeatures(features: features) //... to pass it as a variable to the initializer. 

但是錯誤如下：

無法將類型一個可變參數的「[NodeFeature]」到預期參數類型「NodeFeatures」

Answer 1

不能傳遞數組給一個函數採取可變參數的參數， 或動態地「建立」值參數列表，比較例如 Passing an array to a function with variable number of args in Swift。

不過幸運的是，該類型有另一初始化

public init(rawValue: UInt16) 

，你可以以不同的方式使用。

選項1：使用的整數位掩碼來組裝功能 而不是數組：

var rawFeatures = UInt16(0) 
if condition { 
    rawFeatures |= NodeFeature.relay.rawValue 
} else if condition { 
    rawFeatures |= NodeFeature.proxy.rawValue 
} 
let wrapper = NodeFeatures(rawValue: rawFeatures) 

選項2：保持你的數組，但計算組合原始值 創建NodeFeatures值：

var features = [NodeFeature]() 
if condition { 
    features.append(.relay) 
} else if condition { 
    features.append(.proxy) 
} 

let rawFeatures = features.reduce(0, { $0 | $1.rawValue }) 
let wrapper = NodeFeatures(rawValue: rawFeatures) 

選項3：默認值INE另一個初始化服用數組參數 在擴展：

extension NodeFeatures { 

    public init(features: [NodeFeature]) { 
     let rawValue = features.reduce(0, { $0 | $1.rawValue }) 
     self.init(rawValue: rawValue) 
    } 
} 

現在你可以直接通過您的數組：

var features = [NodeFeature]() 
if condition { 
    features.append(.relay) 
} else if condition { 
    features.append(.proxy) 
} 
let wrapper = NodeFeatures(features: features)