mocking.swift

import Combine


struct Location {
}

//protocol WeatherService {
//  func getTemperature(location: Location) -> AnyPublisher<Double, Error>
//}
//
//final class MockWeather: WeatherService {
//
//  var temperature: Result<Double, Error> = .success(20)
//
//  func getTemperature(location: Location) -> AnyPublisher<Double, Error> {
//    switch temperature {
//    case .success(let temp):
//      return Just(temp)
//        .setFailureType(to: Error.self)
//        .eraseToAnyPublisher()
//    case .failure(let error):
//      return Fail(error: error).eraseToAnyPublisher()
//    }
//  }
//}


struct WeatherService {
  var getTemperature: (Location) -> AnyPublisher<Double, Error>
}

extension WeatherService {
  static func happy(temp: Double) -> Self {
    WeatherService(getTemperature: { location in
    Just(temp).setFailureType(to: Error.self).eraseToAnyPublisher()
    })
  }
}

extension WeatherService {
  static let real = WeatherService(getTemperature: { location in
    Just(20.0).setFailureType(to: Error.self).eraseToAnyPublisher()
  })
}

final class WeatherViewModel: ObservableObject {
  @Published var temperature: Double?
  let service: WeatherService

  init(service: WeatherService) {
    self.service = service
  }
}

WeatherViewModel(service: .happy(temp: 20))
WeatherViewModel(service: .real)


protocol Printable {
  func describe() -> String
}

struct Printing<A> {
  var describe: (A) -> String
}


struct User {
  var login: String
  var email: String


  static let short = Printing<User> { user in
    user.login
  }

  static let long = Printing<User> { user in
    user.login + " " + user.email
  }

}

let ray = User(login: "ray", email: "ray@example.com")

func describe<A>(thing: A, printer: Printing<A>) {
  print(printer.describe(thing))
}

describe(thing: ray, printer: User.short)