optional binding

if let, while let, guard let 的語法統稱為 "optional binding"。

💾 程式

// ⭐️ if let/var
if let x = x { ... }
if var x = x { ... }    // `x` is mutable
if let x { ... }        // ⭐️ Swift 5.7: `= x` omitted

// ⭐️ guard let
guard let x = x else { ... }    // early exit

// ⭐️ while let
while let x = x { ... }

// ⭐️ multiple optional bindings & boolean conditions
if 
    let a = Int("4"),     // optional binding
    let b = Int("42"),    // optional binding
    a < b && b < 100      // boolean condition
{ ... }

// while let
while 
    let cat = cats[i], 
    cat.vaccinated 
{ ... }

⭐️ 重點

optional binding can be used with if and while statements to check for a value inside an optional.

if let vs. guard let

• if let: bound variables are available only within the body of the if statement.

• guard let: bound variables are available in the lines of code that follow the guard statement.

🖥️ 影片

📘 手冊

• Swift ⟩ The Basics ⟩ Optionals ⟩ Optional Binding

📗 參考

• AppCoda ⟩ Swift 5.7 新功能 縮短 Unwrap 的程式碼
• KHAWER KHALIQ ⟩ Unwrapping Optionals With Optional Binding in Swift
• Sundell ⟩ Swift 5.7’s new optional unwrapping syntax (⭐️ Swift 5.7)

👥 相關

• ⭐️ Swift 5.7 - new syntax for optional binding.