Swift 类和函数

Question

我正在学习 swift 类(class)，我必须为此场景编写代码，但我不知道为什么我的函数不起作用。我感到非常恼火。

//: 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()


}

Answer 1

您需要将状态var移动到类定义之后并调用Texas.populationAfter()。对于 State 来说，拥有名为 Texas、Oklahoma 等的属性是没有意义的，但这就是您的代码正在做的事情。在代码中调用 Texas.populationAfter() 是完全非法的，因为代码需要位于函数声明内。

通过将状态的创建移到 State 类之外，您可以使用 State 类定义创建变量，然后您可以调用 名为 Texas 的 State 实例上的populationAfter() 方法。

请注意，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，您的 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!。

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()