Swift类和函数

我正在学习一门关于swift的课程，我必须为这个senario编写一个代码，我不知道为什么我的函数不起作用。我非常恼火

//: Playground - noun: a place where people can play

import Cocoa

// create class

class State
{
    var population: Double?
    var capital: String?
    var name: String?
    var growthRate: Double?
    var nextYearPopulation: Double?
    var neighbors: [State]


// initialize vars
    init(population: Double?, capital: String?, name: String?, growthRate: Double?, neighbors: [State])
    {
        self.population = population
        self.capital = capital
        self.name = name
        self.growthRate = growthRate
        self.neighbors = neighbors
    }

    var Texas = State(population: 1000000, capital: "Austin", name: "Texas", growthRate: 0.012, neighbors: [])

    var Oklahoma = State(population: 3000000, capital: "Oklahoma City", name: "Oklahoma", growthRate: 0.01, neighbors: [])

    var NewMexico = State(population: 1000000, capital: "Santa Fe", name: "New Mexico", growthRate: 0.02, neighbors: [])

    var NewYork = State(population: 25000000, capital: "New York City", name: "New York", growthRate: 0.1, neighbors: [])

    var Virginia = State(population: 15000000, capital: "Richmond", name: "Virginia", growthRate: 0.03, neighbors: [])

    var Florida = State(population: 20000000, capital: "Tallahassee", name: "Florida", growthRate: 0.07, neighbors: [])

    //functions

    func populationAfter()
    {
        nextYearPopulation = self.growthRate! * self.population!
        print("The projected population for ", self.name, "is ", nextYearPopulation)
    }

    Texas.populationAfter()


}

---

您需要将state

var

s和调用

Texas.populationAfter（）

移动到类定义之后。对于

州

来说，拥有名为

德克萨斯州

、

俄克拉荷马州

等的属性是没有意义的，但这就是您的代码所做的。在代码中调用

Texas.populationAfter（）

是完全非法的，因为代码需要在函数声明中

通过将状态的创建移动到

状态

类之外，然后使用

状态

类定义创建变量，然后可以在名为

德克萨斯州

的

状态

实例上调用

populationAfter（）

方法

注意，在Swift中，建议对变量和属性使用以小写字母开头的字符串，对类和结构类型使用以大写字母开头的字符串

请注意，

populationAfter

函数只是计算人口增长。要获得新的更新人口，请乘以

1+self.growthRate取而代之

class State
{
    var population: Double?
    var capital: String?
    var name: String?
    var growthRate: Double?
    var nextYearPopulation: Double?
    var neighbors: [State]

    // initialize vars
    init(population: Double?, capital: String?, name: String?, growthRate: Double?, neighbors: [State])
    {
        self.population = population
        self.capital = capital
        self.name = name
        self.growthRate = growthRate
        self.neighbors = neighbors
    }

    //functions

    func populationAfter()
    {
        nextYearPopulation = (1 + self.growthRate!) * self.population!
        print("The projected population for ", self.name!, "is ", nextYearPopulation!)
    }
}

var Texas = State(population: 1000000, capital: "Austin", name: "Texas", growthRate: 0.012, neighbors: [])

var Oklahoma = State(population: 3000000, capital: "Oklahoma City", name: "Oklahoma", growthRate: 0.01, neighbors: [])

var NewMexico = State(population: 1000000, capital: "Santa Fe", name: "New Mexico", growthRate: 0.02, neighbors: [])

var NewYork = State(population: 25000000, capital: "New York City", name: "New York", growthRate: 0.1, neighbors: [])

var Virginia = State(population: 15000000, capital: "Richmond", name: "Virginia", growthRate: 0.03, neighbors: [])

var Florida = State(population: 20000000, capital: "Tallahassee", name: "Florida", growthRate: 0.07, neighbors: [])

Texas.populationAfter()

为什么它不起作用？它会崩溃吗？或者可能会让你的计算机着火？我的populationAfter（）函数不起作用。你需要更具体一些。你期望从函数中得到什么？你得到了什么？什么都没有发生。它应该计算并打印预期的填充。您应该将您的州和调用移动到
Texas.populationAfter（）
类定义之外。OHHHH所以这是关于程序中的放置顺序！非常感谢你！不是顺序而是包容。花括号是有意义的。在它们内部与在它们外部非常不同。问题是函数调用在类声明块内部，而在声明块中只能声明内容，不能执行任何操作。我还要补充一点，您不需要在类声明外部声明变量，你可以把它们放在那里，但你必须这样称呼它们
State.Texas
，除非一个州没有大写字母、名称或增长率是有效的，否则我建议你避免在这里使用可选变量。它们只是让事情复杂化，因为你必须把它们拆开。使用强制展开
nil
时，code>将导致崩溃。