Class

Using Swift
1

class Country {

init(name: String, capitalCity: City) {

self.name = name

self.capitalCity = capitalCity

}

var name: String

var capitalCity: City

}

class City {

let name: String

let country: Country

init(name: String, country: Country) {

self.name = name

self.country = country

}

}

var country = Country(name: "Canada", capitalName: "Ottawa")

print("(country.name)'s capital city is called (country.capitalCity.name)")

2

hello
For some reasons I can not run these code (any ideas)

3

Please use three backticks ``` to open and close a code block, so it makes it readable. I'll paste your code here for reference:

class Country {
  init(name: String, capitalCity: City) {
    self.name = name

    self.capitalCity = capitalCity
  }

  var name: String

  var capitalCity: City
}

class City {
  let name: String

  let country: Country

  init(name: String, country: Country) {
    self.name = name

    self.country = country
  }
}

var country = Country(name: "Canada", capitalCity: City(name: "Ottawa", country: capitalCity))

country.capitalCity = City(name: "Ottawa", country: country)

print("(country.name)'s capital city is called (country.capitalCity.name)")

The error seems to be that in the line when you're creating a country, that starts with var country = Country(..., you are passing a value called capitalCity to the country: parameter, but no capitalCity is defined before that line.

4

As written this is an impossible infinite recursive data structure. You need to break the cycle, e.g. this will do:

class Country {
    init(name: String, capitalCity: City) {
        self.name = name
        self.capitalCity = capitalCity
    }
    var name: String
    var capitalCity: City
}

class City {
    let name: String
    var country: Country!
    init(name: String, country: Country!) {
        self.name = name
        self.country = country
    }
}

func foo() {
    let capitalCity = City(name: "Ottawa", country: nil)
    let country = Country(name: "Canada", capitalCity: capitalCity)
    capitalCity.country = country
    print("(country.name)'s capital city is called (country.capitalCity.name)")
}

On top of that there's a retain cycle here which might or might not be a problem in your case:

  • if you create a country list once that's not a big deal, as it won't "leak" constantly, just stay in memory until app terminates.
  • if you creating countries / cities dynamically then:
    1. either make one of the references weak (typically links to "parent" are made weak, so in this case the country field of the city class.
    2. or break the link manually when you are about to delete the country.
1 Like
5

thank you very much -> it is running now

6

thank you very much -> it is running now