Calling Types As Functions

讓一般的物件可以像函數一樣，只要給它一些參數，它就可以回傳一些別的東西，用法類似 subscript，只是把 instance[index] 改為 instance(index) 而已。

This feature supports argument labels and parameter types, throws and rethrows, and is not constrained to primary type declarations. Furthermore, it is possible to define multiple callAsFunction methods on a single type, and Swift will handle which one to call, similar to a simple overloading.

📦 User

struct Adder {
    var base: Int
    // ⭐️ callAsFunction 
    func callAsFunction(_ x: Int) -> Int {
        return base + x
    }
}

💈 範例

let add3 = Adder(base: 3)
add3(10)                     // 13 == adder.callAsFunction(10)

📘 參考

• Swift 5.2 Brings callAsFunction, Subscript with Default Arguments, and More - InfoQ

• https://www.raywenderlich.com/9224115-what-s-new-in-swift-5-2

• SE-0253: Callable values of user-defined nominal types

• Swift: subscript vs. callAsFunction - StackOverflow

⚙️ 執行

Online editor and compiler

💈範例

從這個語法看起來，這個就有點像 subscript 一樣，只是把 subscript 的 something[index] 改為 something(index) 而已。

#todo: #if swift>=5.2 寫入 CGRect(x, y)