深入浅出的聊聊Swift高阶函数

struct Student {
    let id: String
    let name: String
    let age: Int
}
 
let stu1 = Student(id: "1001", name: "stu1", age: 12)
let stu2 = Student(id: "1002", name: "stu2", age: 14)
let stu3 = Student(id: "1003", name: "stu3", age: 16)
let stu4 = Student(id: "1004", name: "stu4", age: 20)
let stus = [stu1, stu2, stu3, stu4]
 
let intIds = stus.map { (stu) in
    Int(stu.id)
}
 
print(intIds) //[Optional(1001), Optional(1002), Optional(1003), Optional(1004)]

 let intIds = stus.compactMap { (stu) in
     Int(stu.id)
   }

let dict = ["key1": 10, "key2": nil]
let result = dict.compactMap { $0 }
print(result) //[(key: "key1", value: Optional(10)), (key: "key2", value: nil)]

  print(result) //["key1": 10]
 let result = dict.compactMapValues { $0 }
 print(result) //["key1": 10]

  let scoresByName = ["Henk": [0, 5, 8], "John": [2, 5, 8]]

  let mapped = scoresByName.map { $0.value }
  // [[2, 5, 8], [0, 5, 8]]
  print(mapped)

 let flatMapped = scoresByName.flatMap { $0.value }
  // [2, 5, 8, 0, 5, 8]

let adults = stus.filter { (stu) -> Bool in
        stu.age >= 18
       }
  print(adults) // 数组中只包含stu4 学生

let totalAges = stus.reduce(0) { (result, stu) in
        return result + stu.age
        }
    print(totalAges) // 62

let adults = stus.compactMap { (stu) in
        Int(stu.id)
        }.filter { (id) -> Bool in
           id > 1002
        }
    print(adults) //[1003, 1004]

let totalAge = stus.filter { (stu) -> Bool in
            stu.age > 12
    }.reduce(0) { (result, stu) in
   return result + stu.age
   }
   print(totalAge) // 50