Challenge 2: NetworkResult Error Handling — Solution

sealed class NetworkResult<out T>
data class Success<T>(val data: T) : NetworkResult<T>()
data class Error(val message: String) : NetworkResult<Nothing>()
object Loading : NetworkResult<Nothing>()

suspend fun fetchPosts(api: PostApiService): NetworkResult<List<Post>> {
    return try {
        NetworkResult.Success(api.getPosts())
    } catch (e: IOException) {
        NetworkResult.Error("No internet connection")
    } catch (e: HttpException) {
        NetworkResult.Error("Server error: ${e.code()}")
    }
}

Notes:
- The two catch blocks are ordered as separate, specific exception
  types (not one generic "catch (e: Exception)") so each failure mode
  gets a message that actually helps diagnose it — a user with no
  internet connection sees a different message than one who genuinely
  reached a broken server.
- NetworkResult<out T> being covariant (Kotlin Intermediate Chapter 3)
  is what allows Error("...") — which is really a NetworkResult<Nothing>
  — to be returned directly from a function declared to return
  NetworkResult<List<Post>>. Without "out", this wouldn't compile.
- api.getPosts() is a suspend call; wrapping it in try/catch works
  exactly like wrapping any other suspend function call, since
  fetchPosts itself is also declared suspend.