問題描述

我想讓一個函數在 Swift 中接受任何數字(Int、Float、Double、...)

I want to make a function accept any number (Int, Float, Double, ...) in Swift

func myFunction <T : "What to put here"> (number : T) ->  {
    //...
}

不使用 NSNumber

without using NSNumber

推薦答案

更新: 下面的答案原則上仍然適用，但是 Swift 4 完成了對數字協議的重新設計，以便添加您自己的通常是不必要的.在構建自己的系統之前，請查看標準庫的數字協議.

Update: The answer below still applies in principle, but Swift 4 completed a redesign of the numeric protocols, such that adding your own is often unnecessary. Take a look at the standard library's numeric protocols before you build your own system.

這實際上在 Swift 中是不可能開箱即用的.為此，您需要創建一個新協議，使用您將在泛型函數中使用的任何方法和運算符進行聲明.此過程對您有用，但具體細節將在一定程度上取決于您的通用函數的作用.以下是獲取數字 n 并返回 (n - 1)^2 的函數的方法.

This actually isn't possible out of the box in Swift. To do this you'll need to create a new protocol, declared with whatever methods and operators you're going to use inside your generic function. This process will work for you, but the exact details will depend a little on what your generic function does. Here's how you'd do it for a function that gets a number n and returns (n - 1)^2.

首先，定義您的協議，使用運算符和一個采用 Int 的初始化程序(這樣我們就可以減去一個).

First, define your protocol, with the operators and an initializer that takes an Int (that's so we can subtract one).

protocol NumericType {
    func +(lhs: Self, rhs: Self) -> Self
    func -(lhs: Self, rhs: Self) -> Self
    func *(lhs: Self, rhs: Self) -> Self
    func /(lhs: Self, rhs: Self) -> Self
    func %(lhs: Self, rhs: Self) -> Self
    init(_ v: Int)
}

所有數字類型已經實現了這些，但此時編譯器并不知道它們是否符合新的NumericType 協議.你必須明確這一點——Apple 稱之為通過擴展聲明采用協議".我們將為 Double、Float 和所有整數類型執行此操作:

All of the numeric types already implement these, but at this point the compiler doesn't know that they conform to the new NumericType protocol. You have to make this explicit -- Apple calls this "declaring protocol adoption with an extension." We'll do this for Double, Float, and all the integer types:

extension Double : NumericType { }
extension Float  : NumericType { }
extension Int    : NumericType { }
extension Int8   : NumericType { }
extension Int16  : NumericType { }
extension Int32  : NumericType { }
extension Int64  : NumericType { }
extension UInt   : NumericType { }
extension UInt8  : NumericType { }
extension UInt16 : NumericType { }
extension UInt32 : NumericType { }
extension UInt64 : NumericType { }

現在我們可以編寫我們的實際函數，使用 NumericType 協議作為通用約束.

Now we can write our actual function, using the NumericType protocol as a generic constraint.

func minusOneSquared<T : NumericType> (number : T) -> T {
    let minusOne = number - T(1)
    return minusOne * minusOne
}

minusOneSquared(5)              // 16
minusOneSquared(2.3)            // 1.69
minusOneSquared(2 as UInt64)    // 1

這篇關于Type 應該采用什么協議來讓泛型函數將任何數字類型作為 Swift 中的參數?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！