Swift類和函數

Question

我在swift上學習，我不得不爲這個senario編寫代碼，我不知道爲什麼我的函數不工作。我變得非常惱火。

//: 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

您需要將您的狀態var S和類定義後，打電話給Texas.populationAfter()。 State具有稱爲Texas,Oklahoma等的屬性沒有意義，但這是您的代碼正在執行的操作。在代碼中調用Texas.populationAfter()是完全非法的，因爲代碼需要位於函數聲明中。

通過移動狀態的創建State類以外，你再使用State類定義創建變量，然後你可以調用名爲Texas的State實例populationAfter()方法。

請注意，在Swift中，推薦使用以小寫字母開頭的字符串作爲變量和屬性，以及以大寫字母開頭的字符串作爲類和結構類型。

請注意，您的populationAfter功能只是計算人口增長。要獲得新的更新人口，請改爲乘以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()