Question

我想创建一个泛型函数，根据传递的属性对类数组进行排序。

例如，我有这些类

public class Car {
    var id: Int
    var manufacturer: String
    var variant: String

    init(id: Int, manufacturer: String, variant: String) {
        self.id = id
        self.manufacturer = manufacturer
        self.variant = variant
    }
}

enum Gender {
    case male
    case female
}

public class Person {
    var id: Int
    var name: String
    var age: Int
    var gender: Gender

    init(id: Int, name: String, age: Int, gender: Gender) {
        self.id = id
        self.name = name
        self.age = age
        self.gender = gender
    }
}

这些数组，

let cars = [
    Car(id: 1, manufacturer: "Ford", variant: "Focus"),
    Car(id: 2, manufacturer: "Nissan", variant: "Skyline"),
    Car(id: 3, manufacturer: "Dodge", variant: "Charger"),
    Car(id: 4, manufacturer: "Chevrolet", variant: "Camaro"),
    Car(id: 5, manufacturer: "Ford", variant: "Shelby")
]

let persons = [
    Person(id: 1, name: "Ed Sheeran", age: 26, gender: .male),
    Person(id: 2, name: "Phil Collins", age: 66, gender: .male),
    Person(id: 3, name: "Shakira", age: 40, gender: .female),
    Person(id: 4, name: "Rihanna", age: 25, gender: .female),
    Person(id: 5, name: "Bono", age: 57, gender: .male)
]

如何为数组编写通用扩展，根据传递的属性对其进行排序？（例如，person.sort（名称）或cars.sort（制造商））

谢谢！

Answer 1

从Swift 4开始，您可以定义一个排序方法一个Key-Path Expression作为参数。正如Leo所指出的，这些方法可以更普遍地定义为协议扩展方法（分别用于可变集合和序列）：

extension MutableCollection where Self: RandomAccessCollection {
    // Mutating in-place sort:
    mutating func sort<T: Comparable>(byKeyPath keyPath: KeyPath<Element, T>) {
        sort(by: { $0[keyPath: keyPath] < $1[keyPath: keyPath] })
    }
}

extension Sequence {
    // Non-mutating sort, returning a new array:
    func sorted<T: Comparable>(byKeyPath keyPath: KeyPath<Element, T>) -> [Element] {
        return sorted(by: { $0[keyPath: keyPath] < $1[keyPath: keyPath] })
    }
}

使用示例：

persons.sort(byKeyPath: \.name)
cars.sort(byKeyPath: \.manufacturer)

有关密钥路径表达式的更多信息，请参阅SE-0161 Smart KeyPaths: Better Key-Value Coding for Swift。

Answer 2

在@MartinR answer上扩展以允许增加（<）或减少（>）排序：

extension MutableCollection where Self: RandomAccessCollection {
    mutating func sort<T: Comparable>(_ keyPath: KeyPath<Element, T>, by areInIncreasingOrder: ((T, T) -> Bool) = (<)) {
        sort(by: { areInIncreasingOrder($0[keyPath: keyPath], $1[keyPath: keyPath]) })
    }
}

extension Sequence {
    func sorted<T: Comparable>(_ keyPath: KeyPath<Element, T>, by areInIncreasingOrder: ((T,T)-> Bool) = (<)) -> [Element] {
        sorted(by: { areInIncreasingOrder($0[keyPath: keyPath], $1[keyPath: keyPath]) })
    }
}

people.sorted(\.age)
people.sorted(\.age, by: >)

cars.sorted(\.manufacturer)
cars.sorted(\.manufacturer, by: >)

编辑/更新：

要通过符合Comparable协议的可选属性来对自定义对象进行排序：

extension MutableCollection where Self: RandomAccessCollection {
    mutating func sort<T: Comparable>(_ keyPath: KeyPath<Element, Optional<T>>, by areInIncreasingOrder: ((T, T) -> Bool) = (<)) {
        sort(by: {
            switch ($0[keyPath: keyPath], $1[keyPath: keyPath]) {
            case let (lhs?, rhs?): return areInIncreasingOrder(lhs, rhs)
            case (.none, _): return false
            case (_, .none): return true
            }
        })
    }
}

extension Sequence {
    func sorted<T: Comparable>(_ keyPath: KeyPath<Element, Optional<T>>, by areInIncreasingOrder: ((T,T)-> Bool) = (<)) -> [Element]  {
        sorted(by: {
            switch ($0[keyPath: keyPath], $1[keyPath: keyPath]) {
            case let (lhs?, rhs?): return areInIncreasingOrder(lhs, rhs)
            case (.none, _): return false
            case (_, .none): return true
            }
        })
    }
}

用法：

array.sort(\.optionalStringProperty) {
    $0.localizedStandardCompare($1) == .orderedAscending
}
print(array)

Answer 3

你走了：

extension Array {
    mutating func propertySort<T: Comparable>(_ property: (Element) -> T) {
        sort(by: { property($0) < property($1) })
    }
}

用法：

persons.propertySort({$0.name})

这是一个非变异版本：

func propertySorted<T: Comparable>(_ property: (Element) -> T) -> [Element] {
    return sorted(by: {property($0) < property($1)})
}

正如Leo Dabus指出的那样，您可以将扩展名推广到MutableCollection的任何RandomAccessCollection：

extension MutableCollection where Self : RandomAccessCollection {
    ...

通过属性对类数组进行排序的通用函数

3 个答案: