🔰function as variable

assign function to a variable

Swift ⟩ basic types ⟩ function ⟩ as variable

🧨 雷區

when you assign a function to a variable, you can't use argument labels on calling this function through that variable.

• replit：assign function to variable

// 1. define function "add"
func add(a: Int, b: Int) -> Int {
    let result = a + b
    print(result)
    print(#function)         // "add(a:b:)" (function signature)
    return result
}

// 2. call add() function (with "argument labels")
let n1 = add(a: 2, b: 3)     // 5, "add(a:b:)"

// --------------------------------------------------------------
//
//     let n3 = add(2, 3)    // ⛔ error: missing argument labels 'a:b:' in call
//
// --------------------------------------------------------------

// ⭐️ 3. assign to a variable 
//
let add2 =   add
//        ╰──F.E.──╯  (⭐️ F.E.: function expression)
//
// ⭐️ `add2` is now a "closure". 
//   • share the same function body with `add`.
//   • but can't use "argument labels" when calling it.

// ⭐️ 4. call "add2" function (without "argument labels")
let n2 = add2(5, 6)                 // 11, "add(a:b:)"

// --------------------------------------------------------------
//
//     let n4 = add2(a: 5, b: 6)    // ⛔ error: extraneous argument labels 'a:b:' in call
//                                  //    (extraneous: 無關的)
// --------------------------------------------------------------

// function type
print(type(of: add))    // (Int, Int) -> Int
print(type(of: add2))   // (Int, Int) -> Int

👥 相關

• closure

🗣 討論

• TreeHouse ⟩ Assigning functions to variables in Swift

• Extraneous argument label 'number:' in call ⭐️

• Can I print function type in Swift? ⭐️ - type(of:), #function (inside function body)

• Weird value of #function literal in Swift 3.1 ⭐️ - #function literal

📗 參考

• Parsing and evaluating expressions using ANTLR in Swift

📘 手冊

• Swift ⟩

  • type(of:)

  • Closures

• Swift Reference ⟩

  • Expressions ⟩ Primary Expressions ⟩ Literal Expression ⟩ #function ⭐️

❓

does Swift have concept of "function expression" like in JS?