在struct或class的顶层，只允许定义函数和属性。例如，let make:String = "MINI"或func getDetails() -> String { ... }是有效的顶层声明。
但是，不允许将不定义函数或属性（如print("")）的命令式代码放在这样的类型的顶层。
如果你是在Swift游戏场，你可以把命令式代码放在文件的顶层（而不是结构体或类的顶层），所以，这是有效的：

struct Car {
    let make:String = "MINI"
    let model:String = "COOPER"
    let year:String = "2015"
    
    var details:String {
        return year + " " + make + " " + model
    }
    func getDetails() -> String {
        return details
    }
}

let myCar = Car()
print(myCar.getDetails())

由于getDetails只返回details，所以这有点多余，所以我们可以重构为：

struct Car {
    let make:String = "MINI"
    let model:String = "COOPER"
    let year:String = "2015"
    
    var details:String {
        return year + " " + make + " " + model
    }
}

let myCar = Car()
print(myCar.details)

import UIKit
import Foundation
struct Car {
   private var make = "Toyota"
  private  var model = "Camry"
    private var year = "1999"
   private var details:String {
        year + " " + make + " " + model
    }
  func getDetails () -> String {
    return details
 }
}
let a:Car = Car()
print (a.getDetails())