swift 5.2更新内容

Swift 5.2 Released!

SE-0249:将Key Path表达式作为函数:(Root)->Value

//    已知结构体

struct User {

    let email: String

    let isAdmin: Bool

}

 生成一个邮箱地址的数组，过滤管理员，管理员数组

users.map { $0.email } 

users.filter { $0.isAdmin }

users.compactMap { $0.isAdmin }

采用新的表达式：\Root.value

users.map(\.email)

users.filter(\.isAdmian)

语法解释：\Root.value相当于{$0[keyPath: \Root.value]}

users.map(\.email) === user.map { $0[keyPath: \User.email] }

语法注意：\Root.value是方法(Root)->Value的缩写，当使用临时变量时：

let kp = \User.email        //    错误❌

let kp: (User) -> String = \User.email    //    正确

let kp = \User.email as (User) -> String    //    正确

users.map(kp)

编译器做了什么？

let kp: (User) -> String = \User.email  //  代码

let kp: (User) -> String = { kp in { root in root[keyPath: kp] } }(\User.email)  //  编译器后的代码

swift为啥添加该语法？

This is a purely additive change and has no impact.//

SE-0253:静态方法自定义

callAsFunction:

struct Adder {

    var base: Int

    func callAsFunction(_ x: Int) -> Int {

        return base + x

    }

    func callAsFunction(_ x: T, bang: Bool) throws -> T where T: BinaryInteger {

        if bang { return T(Int(exactly: x)! + base) }

        else { retuurn T(Int(truncatingIfNeeded: x) + base) }

    }

}

let add = Adder(base: 3)

add(10)    // => 13

try add(4, bang: true) // => 5

subscript:

struct Polynomial {

    let coefficients: [Float]

}

extension Polynomial {

    subscript(input: Float) -> Float {

        var result: Float = 0

        for (i, c) in coefficients.enumerated() {

            result += c * pow(input, Float(i))

        }

        return result

    }

}

let polynomial = Polynomial(coefficients: [2, 3, 4])

print(polynomial.evaluated(at: 2)) // => 24

与闭包结合：类似于代理

struct BoundClosure ()>: () -> () {

    var function: F

    var value: T

    func callAsFunction() { return function(value) }

}

let f = BoundClosure({ print($0) }, x) // instantiates BoundClosure<(underlying type of closure), Int>

f() // invokes call on BoundClosure

提高编译结果准确性：错误代码提示更准确

优化代码不全：代码提示更人性化

优化编译算法

· Whole Module (typically used for Release builds)

· Incremental (typically used for Debug builds)