Question

我对Swift很新，但我无法解决这个问题。我需要计算结构中创建的实例数。由于我创建了3个实例，我怎样才能让程序告诉我有三个实例？我最后尝试了exNames.count，但那不起作用......谢谢！

struct People {
    let name: String
    var age: Int
    let sex: Character
}

var heather = People(name: "Heather", age: 32, sex: "F")
var peter = People(name: "Peter", age: 34, sex: "M")
var scott = People(name: "Scott", age: 27, sex: "M")

let exNames = [People]()

exNames.count

Answer 1

您想在People结构上使用静态变量。但是，这确实需要覆盖默认初始值设定项。

struct People
{
    static var instances = 0

    let name:String
    var age:Int
    let sex:Character

    init(name:String, age:Int, sex:Character)
    {
        self.name = name
        self.age = age
        self.sex = sex

        People.instances += 1
    }
}

var heather = People(name: "Heather", age: 32, sex: "F")
var peter = People(name: "Peter", age: 34, sex: "M")
var scott = People(name: "Scott", age: 27, sex: "M")

let exNames = [People]() 
/* exNames.count only gives the number of People that are 
contained in this particular array, which is zero. */

print(People.instances) // 3

如果您希望在struct超出范围时减少计数，则需要升级到提供取消初始化class的{{1}}

请注意，静态计数器的“正确”用例非常有限。你实际上试图解决的问题很可能会被另一把锤子更好地服务。

顺便说一句，你真的不应该使用deinit {}来表示Character，因为Swift中的sex与字符串紧密相关，因此它们是为了构建和优化的词汇目的，而不是标记。它还为很多潜在的错误打开了大门，因为Swift也无法验证有效输入（如果有人意外传递了Character sex的值，该怎么办？）相反，请使用如果您需要更多功能，则内置"@"类型或自定义Bool。

Answer 2

在这种情况下，您似乎想创建一组人：

struct People {
    let name: String
    var age: Int
    let sex: Character
}

var heather = People(name: "Heather", age: 32, sex: "F")
var peter = People(name: "Peter", age: 34, sex: "M")
var scott = People(name: "Scott", age: 27, sex: "M")

//This should be a var, because you are going to modify it
var exNames = [People]()

exNames.append(heather)
exNames.append(peter)
exNames.append(scott)

exNames.count

计算swift中结构内的实例数

2 个答案: