Swift vs Kotlin Comparison

// Swift - Modern concurrent data loading
import Foundation

// Thread-safe data manager with actor
actor UserDataManager {
    private var cache: [String: User] = [:]

    func fetchUser(id: String) async throws -> User {
        if let cached = cache[id] {
            return cached
        }

        let url = URL(string: "https://api.example.com/users/\\(id)")!
        let (data, response) = try await URLSession.shared.data(from: url)

        guard let httpResponse = response as? HTTPURLResponse,
              httpResponse.statusCode == 200 else {
            throw APIError.invalidResponse
        }

        let user = try JSONDecoder().decode(User.self, from: data)
        cache[id] = user
        return user
    }
}

// Usage
struct User: Codable {
    let id: String
    let name: String
    let email: String
}

enum APIError: Error {
    case invalidResponse
    case notFound
}

// Inside a SwiftUI View
@Observable class ProfileViewModel {
    var user: User?
    var isLoading = false
    var errorMessage: String?
    private let manager = UserDataManager()

    func loadUser(id: String) async {
        isLoading = true
        defer { isLoading = false }
        do {
            user = try await manager.fetchUser(id: id)
        } catch {
            errorMessage = error.localizedDescription
        }
    }
}

// Kotlin - Modern concurrent data loading
import kotlinx.coroutines.*
import kotlinx.serialization.*
import kotlinx.serialization.json.*

@Serializable
data class User(
    val id: String,
    val name: String,
    val email: String
)

sealed class Result<out T> {
    data class Success<T>(val data: T) : Result<T>()
    data class Error(val exception: Exception) : Result<Nothing>()
}

class UserRepository(private val httpClient: HttpClient) {
    private val cache = mutableMapOf<String, User>()

    suspend fun fetchUser(id: String): Result<User> {
        cache[id]?.let { return Result.Success(it) }

        return try {
            val user = httpClient.get<User>("https://api.example.com/users/$id")
            cache[id] = user
            Result.Success(user)
        } catch (e: Exception) {
            Result.Error(e)
        }
    }
}

// ViewModel (Android)
class ProfileViewModel(
    private val repository: UserRepository
) : ViewModel() {

    private val _uiState = MutableStateFlow<UiState>(UiState.Loading)
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()

    fun loadUser(id: String) {
        viewModelScope.launch {
            _uiState.value = UiState.Loading
            _uiState.value = when (val result = repository.fetchUser(id)) {
                is Result.Success -> UiState.Success(result.data)
                is Result.Error -> UiState.Error(result.exception.message ?: "Unknown error")
            }
        }
    }

    sealed class UiState {
        object Loading : UiState()
        data class Success(val user: User) : UiState()
        data class Error(val message: String) : UiState()
    }
}