Swift 中函数的初始化和 class 继承如何工作

Question

基于 JavaScript 代码中的示例，我想在 Swift 中应用相同的步骤。如果你能帮助我了解它如何工作以获得所有形状的面积。

试图用下面的代码解决它，但是它不起作用。

class Shape {
    func getArea() {
    }
}

class Square: Shape {
    var a: Double
    init(a: Double) {
        self.a = a
        super.init()
    }
    override func getArea() {
        a * a
    }
}

class Rectangle: Shape {
    var a: Double
    var b: Double
    init(a: Double, b: Double) {
        self.a = a
        self.b = b
        super.init()
    }
    override func getArea() {
        a * b
    }
}

class Circle: Shape {
    var r: Double
    init(r: Double) {
        self.r = r
        super.init()
    }
    override func getArea() {
        r * r * Double.pi
    }
}

let square = Square(a: 1.1)
let rectangle = Rectangle(a: 5.0, b: 9.1)
let circle = Circle(r: 2.3)
let shapes = [square, rectangle, circle]

func getTotalArea() -> Double {
    
    let areas = shapes.map { [=12=].getArea() }
    
    let sum = areas.reduce (1, +)
    
    return sum
}

let shapesArea = getTotalArea()
print(shapesArea)

Answer 1

getArea 没有 return 任何东西。您必须定义 getArea() -> Double。此外，Shape 应该是一个没有实现（没有大括号）的 func getArea() -> Double 协议。

另请注意，减少（求和）区域时，必须从0开始，而不是从1开始。

protocol Shape {
    func getArea() -> Double
}

class Square: Shape {
    var a: Double
    init(a: Double) {
        self.a = a
    }
    func getArea() -> Double {
        a * a
    }
}

class Rectangle: Shape {
    var a: Double
    var b: Double
    init(a: Double, b: Double) {
        self.a = a
        self.b = b
    }
    func getArea() -> Double {
        a * b
    }
}

class Circle: Shape {
    var r: Double
    init(r: Double) {
        self.r = r
    }
    func getArea() -> Double {
        r * r * Double.pi
    }
}

let square = Square(a: 1.1)
let rectangle = Rectangle(a: 5.0, b: 9.1)
let circle = Circle(r: 2.3)
let shapes: [Shape] = [square, rectangle, circle]

func getTotalArea() -> Double {

    let areas = shapes.map { [=10=].getArea() }

    let sum = areas.reduce(0, +)

    return sum
}

let shapesArea = getTotalArea()
print(shapesArea)

一个更“敏捷”的解决方案是使用结构，使用它们自动生成的初始化，area 作为计算属性:

protocol Shape {
    var area: Double { get }
}

struct Square: Shape {
    var a: Double
    var area: Double {
        a * a
    }
}

struct Rectangle: Shape {
    var a: Double
    var b: Double

    var area: Double {
        a * b
    }
}

struct Circle: Shape {
    var r: Double
    var area: Double {
        r * r * .pi
    }
}

let square = Square(a: 1.1)
let rectangle = Rectangle(a: 5.0, b: 9.1)
let circle = Circle(r: 2.3)
let shapes: [Shape] = [square, rectangle, circle]

func getTotalArea() -> Double {
    return shapes
       .map { [=11=].area }
       .reduce(0, +)
}

let shapesArea = getTotalArea()
print(shapesArea)

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