📘for...in

Swift ⟩ flow control ⟩ loop ⟩ for...in

• ✅ continue: skip to the next element.

• ✅ break: break the iteration completely. 👉 1️

• ❌ return: invalid outside of a function.

📗 參考

• Advanced Swift, p.

• Sundell ⟩ Picking between a for loop and forEach

• Sarun ⟩ How to get index and value from for loop in Swift

1

👉 replit

var a1 = [Int]()
var a2 = [Int]()
var a3 = [Int]()
var a4 = [Int]()
var a5 = [Int]()

/*
    for-in loop
    -----------
    - ✅ continue: skip to next element
    - ✅ break   : break the loop completely
    - ❌ return  : invalid outside of a function
*/

// 'break' in for-in loop
for n in 1...10 {
    if n > 3 { break }  // ⭐ break for-loop completely
    a1.append(n) 
}
// ⭐ [1, 2, 3]

print(a1)

/*
    .forEach()
    -----------
    - ⛔ continue: not allowed
    - ⛔ break   : not allowed
    - ❗ return  : return from closure only
*/

// early 'return' in forEach
(1...10).forEach { n in 
    if n > 2 { return }     // ⭐ early return
    a2.append(n)            // ⭐ number NOT appended
}
// ⭐ [1, 2]

// late 'return' in forEach
(1...10).forEach { n in 
    a3.append(n)            // ⭐ number appended
    if n > 2 { return }     // ⭐ late return from closure
}
// ⭐ [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

// ⛔ 'continue' in forEach not allowed
(1...10).forEach { n in 
    // ⛔ error: 'continue' is only allowed inside a loop
    if n > 2 { continue }     
    a4.append(n)
}

// ⛔ 'break' in forEach not allowed
(1...10).forEach { n in 
    // ⛔ error: 
    //  - unlabeled 'break' is only allowed inside a loop or switch
    //  - labeled 'break' is required to exit an `if` or `do`
    if n > 2 { break }     
    a5.append(n)
}

2

// for ... in ... where ...
for article in articles where !article.isDraft {  // ⭐️ where clause
    results.append(article)
    guard results.count < 5 else { break }  // ⭐️ break for-loop entirely
}

📘 手冊

• Collections ⟩ Sequence ⟩ .forEach(_:)

• Flow Control ⟩ for-in loop - iterate over a sequence (array, range, string, dictionary)

👥 相關

• seq.forEach() ⭐️