Swift -如何映射数组到字典值?

Question

我想象类似这样的代码:

var someDict: [Int:Bool] = { (0...100).map { someInt -> [Int: String] in (someInt:false) } }

，但它不工作:(

如何正确映射数组的一些值字典?

Answer 1

您可以使用的最少的语法包括AnyIterator来无限地重复一个值。

Dictionary(uniqueKeysWithValues: zip(0...100, AnyIterator { false }))

Answer 2

您可以这样使用reduce:

let someDict = (0...100).reduce(into: [Int: Bool]()) { $0[$1] = false }

Answer 3

基于 jesse的答案的答案, dillon-mce and Joakim Danielson非常感谢!

这是必要的，因为init的语法很糟糕，默认值

extension Dictionary {
    init<S: Sequence>(_ keys: S, withVal defaultVal: Value) where S.Element == Key {
        self = Dictionary( uniqueKeysWithValues: zip(keys, AnyIterator { defaultVal }) )
    }
}

用法:

//enum FileFilterMode: CaseIterable
let a = Dictionary(FileFilterMode.allCases, withVal: false)
let b = Dictionary(0...100, withVal: false)

<标题>的另一种方式:

public extension Sequence {
    func toDict<Key: Hashable, Value>(block: (Element)->(Value)) -> [Key:Value] where Key == Self.Element {
        self.toDict(key: .self, block: block)
    }
    
    func toDict<Key: Hashable, Value>(key: KeyPath<Element, Key>, block: (Element)->(Value)) -> [Key:Value] {
        var dict: [Key:Value] = [:]
        
        for element in self {
            let key = element[keyPath: key]
            let value = block(element)
            
            dict[key] = value
        }
        
        return dict
    }
}

会给你施展魔法的能力，比如:

// dict's keys 0...100 will have value "false"
let a = (0...100).toDict() { _ in false }
// set of tuples -> dict[ $0.0 : $0.1 ]
let b = setOfTuples.toDict( key: .0 ) { _ in $0.1 }