Swift mutating function struct pass struct’s variable name in function? - swift

Question

I am working in Swift trying to update an organization struct that will need to hold a latitude and longitude. I created a mutating function in the struct that will update the latitude and longitude based on the organization organization struct’s address. I got it to work, but the issue is that when I call the mutating function, I need to manually enter the variable name with the .latitude and .longitude. Is there a way that I can pass the variable struct’s name automatically and reference the .latitude and .longitude without calling the specific variable name with it so I can make it more usable? I included an example below with my code. Thanks for your help!
import UIKit
import PlaygroundSupport
import CoreLocation
PlaygroundPage.current.needsIndefiniteExecution = true
struct organization {
var name: String
var address: String
var latitude: CLLocationDegrees = 0 //default setting for latitude
var longitude: CLLocationDegrees = 0 //default setting for longitude
mutating func getCoordinateFrom(completion: #escaping(_ coordinate: CLLocationCoordinate2D?, _ error: Error?) -> () ) {
CLGeocoder().geocodeAddressString(address) { placemarks, error in
completion(placemarks?.first?.location?.coordinate, error)
}
}
}
struct Coordinates {
var latitude: Double
var longitude: Double
}
//create an wildernessLodge variable of type organization
var wildernessLodge = organization(name: "Disney's Wilderness Lodge", address: "901 Timberline Dr, Orlando, FL 32830")
wildernessLodge.getCoordinateFrom { coordinate, error in
guard let coordinate = coordinate, error == nil else { return }
wildernessLodge.latitude = coordinate.latitude
wildernessLodge.longitude = coordinate.longitude
print("update 1 \(wildernessLodge)")
}

Answer 1

I'm a bit confused by your code. Why is getCoordinateFrom marked as mutating? Perhaps you meant to write something like this.
mutating func getCoordinatesFromAddress() {
CLGeocoder().geocodeAddressString(address) { placemarks, error in
guard let coordinate = placemarks?.first?.location?.coordinate, error == nil else { return }
self.latitude = coordinate.latitude
self.longitude = coordinate.longitude
}
}
Now this function is mutating (it modifies self), and
wildernessLodge.getCoordinateFrom { coordinate, error in ... }
can be replaced with
wildernessLodge.getCoordinatesFromAddress()
The only reason to leave the getCoordinateFrom method is if, somewhere in your code, you intend to get coordinates from an address but not update the coordinates in the struct. I can't imagine a good reason to do that, so I would recommend replacing the getCoordinateFrom method with something else.
Alternatively, if you generally intend to set the coordinates right after creating a value of this type, you might want to consider something like this.
init(name: String, address: String) {
self.name = name
self.address = address
CLGeocoder().geocodeAddressString(address) { placemarks, error in
guard let coordinate = placemarks?.first?.location?.coordinate, error == nil else { return }
self.latitude = coordinate.latitude
self.longitude = coordinate.longitude
}
}
or
init(name: String, address: String) {
self.name = name
self.address = address
self.getCoordinatesFromAddress()
}
Then, you could create an organization using organization(name: name, address: address) and the coordinates would automatically be set correctly.
If neither of these are satisfactory, maybe you should create two different structs to capture the behavior you want.
struct Organization {
var name: String
var address: String
func withCoordinates(completion: #escaping(_ coordinate: CLLocationCoordinate2D?, _ error: Error?) -> () ) {
CLGeocoder().geocodeAddressString(address) { placemarks, error in
completion(placemarks?.first?.location?.coordinate, error)
}
}
}
struct OrganizationWithCoordinates {
var name: String
var address: String
var latitude: CLLocationDegrees
var longitude: CLLocationDegrees
init(from organization: Organization) {
self.name = organization.name
self.address = organization.address
organization.withCoordinates { coordinate, error in
guard let coordinate = coordinate, error == nil else { return }
self.latitude = coordinate.latitude
self.longitude = coordinate.longitude
}
}
}
I would prefer an approach like this, but I like having lots of types.
Finally, as noted in the comments, if you are really just concerned with brevity, you can replace
var latitude: CLLocationDegrees
var longitude: CLLocationDegrees
with
var coordinates: CLLocationCoordinate2D
var latitude: CLLocationDegrees { coordinates.latitude }
var longitude: CLLocationDegrees { coordinates.longitude }
and then replace
wildernessLodge.latitude = coordinate.latitude
wildernessLodge.longitude = coordinate.longitude
with
wildernessLodge.coordinates = coordinate
In fact, you should feel free to combine any of these approaches.
Edit: As pointed out, these solutions do not work as-is. The fundamental tension is trying to work with CLGeocoder's async method synchronously. One solution is to use a class instead of a struct. The other approach is to use a modification of the withCoordinate method above:
struct Organization {
var name: String
var address: String
func withCoordinate(callback: #escaping (OrganizationWithCoordinate?, Error?) -> Void) {
CLGeocoder().geocodeAddressString(self.address) { placemarks, error in
if let coordinate = placemarks?.first?.location?.coordinate, error == nil {
let orgWithCoord = OrganizationWithCoordinate(name: self.name, address: self.address, latitude: coordinate.latitude, longitude: coordinate.latitude)
callback(orgWithCoord, nil)
} else {
callback(nil, error)
}
}
}
}
struct OrganizationWithCoordinate {
var name: String
var address: String
var latitude: CLLocationDegrees
var longitude: CLLocationDegrees
}
Organization(name: "Disney's Wilderness Lodge", address: "901 Timberline Dr, Orlando, FL 32830").withCoordinate { orgWithCoord, error in
guard let orgWithCoord = orgWithCoord, error == nil else {
print("Error")
return
}
print(orgWithCoord)
}
This embraces the async nature of CLGeocoder.
Another solution could be to force CLGeocoder to be synchronous using DispatchSemaphore as follows. I don't think these work correctly in Playgrounds, but this should work in an actual app.
struct Organization {
var name: String
var address: String
var latitude: CLLocationDegrees
var longitude: CLLocationDegrees
init(name: String, address: String) throws {
self.name = name
self.address = address
var tempCoordinate: CLLocationCoordinate2D?
var tempError: Error?
let sema = DispatchSemaphore(value: 0)
CLGeocoder().geocodeAddressString(address) { placemarks, error in
tempCoordinate = placemarks?.first?.location?.coordinate
tempError = error
sema.signal()
}
// Warning: Will lock if called on DispatchQueue.main
sema.wait()
if let error = tempError {
throw error
}
guard let coordinate = tempCoordinate else {
throw NSError(domain: "Replace me", code: -1, userInfo: nil)
}
self.longitude = coordinate.longitude
self.latitude = coordinate.latitude
}
}
// Somewhere in your app
let queue = DispatchQueue(label: "Some queue")
queue.async {
let wildernessLodge = try! Organization(name: "Disney's Wilderness Lodge", address: "901 Timberline Dr, Orlando, FL 32830")
DispatchQueue.main.async {
print(wildernessLodge)
}
}
Here, a new queue to do Organization related work is created to avoid locking up the main queue. This method creates the least clunky-looking code in my opinion, but probably is not the most performant option. The location APIs are async for a reason.