Swiftda Closures

Swiftda, closure — bu nomsiz funksiyaga o'xshash maxsus kod bloki. Masalan,

Swift•

Oddiy closure

let greet = {
print("Hello World!")
}

greet()

Bu yerda Hello World chiqaradigan closure yaratilgan.

Closure haqida o'rganishdan oldin Swift funksiyalarini bilish muhim.

Closure e'lon qilish

Closure yaratishda func kalit so'zi ishlatilmaydi. Sintaksis quyidagicha:

{ (parameters) -> returnType in
   // operatorlar
}

Bu yerda:

parameters — closure qabul qiladigan qiymatlar
returnType — closure qaytaradigan qiymat turi
in — parametrlar/qaytish turini closure tanasidan ajratadi

Misol:

Swift•

Parametrli Closure

let example = { (name: String) -> String in
  return "Hello, \(name)"
}

print(example("Swift"))

Closure parametrlari

Closure ham parametr qabul qilishi mumkin:

Swift•

Parametrli Closure

// bitta parametr qabul qiladigan closure
let greetUser = { (name: String) in
  print("Salom, \(name).")
}

// closure chaqirish
greetUser("Delilah")

E'tibor bering:

(name: String) — parametr
in — parametrlar va closure tanasini ajratadi
greetUser("Delilah") — parametr nomi yozilmaydi

Qiymat qaytaradigan Closure

Closure qiymat qaytarishi ham mumkin:

Swift•

Qiymat qaytaradigan Closure

// closure e'loni
let findSquare = { (num: Int) -> Int in
let square = num * num
return square
}

// closure chaqirish
let result = findSquare(3)

print("Kvadrat:", result)

Tushuntirish:

(num: Int) — parametr
-> Int — qaytish turi
return square — qaytariladigan qiymat

Closureni funksiya parametri sifatida yuborish

Swiftda closureni funksiyaga parametr qilib berish mumkin:

Swift•

Closure parametri

// funksiya e'loni
func grabLunch(search: () -> ()) {
print("Keling, tushlikka chiqamiz")

// closure chaqirish
search()
}

// parametr sifatida closure berish
grabLunch(search: {
 print("Alfredo's Pizza: 2 mil uzoqlikda")
})

Bu yerda:

search — funksiya parametri
() -> () — closure turi
search() — closure chaqirilyapti

Trailing Closure

Agar funksiya oxirgi parametr sifatida closure qabul qilsa:

Swift•

Trailing Closure

func grabLunch(message: String, search: ()->()) {
 print(message)
 search()
}

// trailing closure ishlatish
grabLunch(message: "Keling, tushlikka chiqamiz")  {
print("Alfredo's Pizza: 2 mil uzoqlikda")
}

Bu yerda closure oxirgi parametr bo'lgani uchun trailing closure shaklida yozildi.

Autoclosure

Funksiya chaqirilayotganda closure'ni {} ishlatmasdan berish mumkin:

Swift•

Autoclosure

// avtomatik closure funksiyasi
func display(greet: @autoclosure () -> ()) {
greet()
}

// {} ishlatmasdan closure berish
display(greet: print("Hello World!"))

@autoclosure — avtomatik ravishda {} qo'shib beradi.

Eslatma: autoclosure parametr qabul qila olmaydi.

Shorthand argument nomlari

Swiftda closure argumentlarini $0, $1, $2 kabi qisqa nomlash mumkin:

Swift•

Shorthand arguments

let numbers = [1, 2, 3, 4, 5]

// To'liq yozuv
let doubled1 = numbers.map { (num: Int) -> Int in
  return num * 2
}

// Qisqa yozuv
let doubled2 = numbers.map { $0 * 2 }

print("To'liq:", doubled1)
print("Qisqa:", doubled2)

Birinchi masalaning yechimi

Keling, birinchi masala "Oddiy closure" ni birga yechib ko'ramiz:

1-qadam: Masalani tushunish

5, 3 → 5 + 3 = 8
10, 20 → 10 + 20 = 30

2-qadam: Yechim algoritmi

Ikki Int parametr qabul qiladigan closure yaratamiz
Ularni qo'shamiz
Natijani qaytaramiz

3-qadam: Kodni yozamiz

Swift•

Oddiy closure yechimi

let add: (Int, Int) -> Int = { (a, b) in
  return a + b
}

// Test
print(add(5, 3))    // 8
print(add(10, 20))  // 30
print(add(-5, 5))   // 0

Qisqa yozuv:

Swift•

Qisqa yozuv

let add: (Int, Int) -> Int = { $0 + $1 }

print(add(5, 3))  // 8

Natija: Closure orqali oddiy qo'shish operatsiyasini yaratdik.