Swift Basic: Only in Swift

Underscore: _

“ignore this”
Underscroe is used to define the parameter is not named.
In for-loop, “no index, just repeat.”

reference

• What is _: in Swift telling me?
• Swift underscore(_)
• Why do I need underscores in swift?

Struct vs Class

: In Swift, struct and class have a lot in common.

• init()
• extension
• protocol
• subscript
• property & method

Then, when should I use struct or class? I learned this from the example below.

• In my project Somking Area v1.0.0, there are 2 variables and 1 function related to loaction.
  • Address struct: has the information about locality and administrative area name.
  • CLLocationCoordinate2D: store the latitude & longitude of the location.
  • getCoordinateToAddress(coordinate: CLLocationCoordinate2D): get locality and adminitrative area name from the coordinate.

  Therefore, I decided to combine the above three things as a single data structure. Location information is the Model in the project, so I tried to implement these as a struct.

struct Location {
    internal init(coordinate: CLLocationCoordinate2D, administrativeArea: String, locality: String) {
        self.coordinate = coordinate
        self.administrativeArea = administrativeArea
        self.locality = locality
    }
    init(coordinate: CLLocationCoordinate2D) {
        self.coordinate = coordinate
        self.administrativeArea = ""
        self.locality = ""
        
        exchangeCoordinateToAddress(coordinate: coordinate) {
          (address) in
            self.administrativeArea = address.administrativeArea
            self.locality = address.locality   
        }
    }

    var coordinate: CLLocationCoordinate2D
    var administrativeArea: String
    var locality: String
    
    func exchangeCoordinateToAddress(coordinate: CLLocationCoordinate2D, completion: @escaping ((Address)->()))  {
      ......
    }
}

Above code did not work(Swift Error Note) because the struct is the value type, so exchangeCoordinateToAddress() method called in init() did not work.

So, class should be used in these cases,

• When you want to change the value. (call by reference)
• inheritance
• type casting

Most of other cases, there would be no problem to use struct.

reference

• Struct, Class