仅阅读属性

Question

我需要在swift中"只读"的帮助。我尝试了各种方法，但根本无法弄清楚如何在没有错误的情况下进行编译。这是我的想法。

创建一个名为iSequiral的纯计算属性，该属性检查三角形的所有三个侧面是否相同，如果不是，则返回true，如果不是。

var isEquilateral: Int {
}

Answer 1

如果您想要"只读"存储的属性，请使用 private(set)：

private(set) var isEquilateral = false

如果它是从其他属性计算的属性，那么，是的，使用计算属性：

var isEquilateral: Bool {
    return a == b && b == c
}

---

为了完整，可能不必说，如果是常数，则只需使用let：

let isEquilateral = true

或

struct Triangle {
    let a: Double
    let b: Double
    let c: Double
    let isEquilateral: Bool
    init(a: Double, b: Double, c: Double) {
        self.a = a
        self.b = b
        self.c = c
        isEquilateral = (a == b) && (b == c)
    }
}

Answer 2

类似的东西？（如 @vacawama 在评论中所建议的那样）

struct Triangle {
    let edgeA: Int
    let edgeB: Int
    let edgeC: Int
    var isEquilateral: Bool {
        return (edgeA, edgeB) == (edgeB, edgeC)
    }
}

让我们测试

let triangle = Triangle(edgeA: 5, edgeB: 5, edgeC: 5)
triangle.isEquilateral // true

或

let triangle = Triangle(edgeA: 2, edgeB: 2, edgeC: 1)
triangle.isEquilateral // false

Answer 3

只读属性是具有getter但没有setter的属性。它总是用于返回值。

class ClassA {
    var one: Int {
        return 1
    }
    var two: Int {
        get { return 2 }
    }
    private(set) var three:Int = 3
    init() {
        one = 1//Cannot assign to property: 'one' is a get-only property
        two = 2//Cannot assign to property: 'two' is a get-only property
        three = 3//allowed to write
        print(one)//allowed to read
        print(two)//allowed to read
        print(three)//allowed to read
    }
}
class ClassB {
    init() {
        var a = ClassA()
        a.one = 1//Cannot assign to property: 'one' is a get-only property
        a.two = 2//Cannot assign to property: 'two' is a get-only property
        a.three = 3//Cannot assign to property: 'three' setter is inaccessible
        print(a.one)//allowed to read
        print(a.two)//allowed to read
        print(a.three)//allowed to read
    }
}