Swift 进阶 —— map 和 flatMap的使用

func getInfos(by name: String) -> [String] {
 if name == "Jack" {
 return ["Male", "25", "New York"]
 } else if name == "Lucy" {
 return ["Female", "18", "London"]
 } else {
 return ["Unkown", "Unkown", "Unkown"]
 }
}

let names = ["Jack", "Lucy", "Nobody"]

let infos1 = names.map { getInfos(by: $0) }
print(infos1)

let infos2 = names.flatMap { getInfos(by: $0) }
print(infos2)

[["Male", "25", "New York"], ["Female", "18", "London"], ["Unkown", "Unkown", "Unkown"]]

["Male", "25", "New York", "Female", "18", "London", "Unkown", "Unkown", "Unkown"]

extension Array {
 func map<T>(_ transfORM: (Element) -> T) -> [T] {
 var result: [T] = []
 for x in self {
  result.append(transform(x))
 }
 return result
 }
}

extension Array {
 func flatMap<T>(_ transform: (Element) -> [T]) -> [T] {
 var result: [T] = []
 for x in self {
  result.append(contentsOf: transform(x))
 }
 return result
 }
}

let stringNumbers = ["1", "2", "3", "foo"]
let x = stringNumbers.first.map { Int($0) } // Optional(Optional(1))
let y = stringNumbers.first.flatMap { Int($0) } // Optional(1)

extension Optional {
 func map<U>(transform: (Wrapped) -> U) -> U? {
 if let value = self {
  return transform(value)
 }
 return nil
 }
}

extension Optional {
 func flatMap<U>(transform: (Wrapped) -> U?) -> U? {
 if let value = self, let transformed = transform(value) {
  return transformed
 }
 return nil
 }
}