Hey guys! I would like to make a mapper from a `HttpResponse` to a `Result<T>` But I can't get...

# ktor

[Stefan de Kraker]

Hey guys! I would like to make a mapper from a HttpResponse to a Result<T> But I can't get it to work?!

class ResponseMapper {
    fun <T> map (httpResponse: HttpResponse) : Result<T> {
        return if (httpResponse.status.isSuccess()){
            Result.success(httpResponse.body()) // This is not allowed?
        } else if (httpResponse.status.value == 401) {
            Result.failure(exception = AuthException())
        } else {
            Result.failure(BackendException(errorCode = httpResponse.status.value))
        }
    }
}

Cannot use 'T' as reified type parameter. Use a class instead.

[Landry Norris]

Can you make this method inline? You'll need it to be inline so it can get the type.

[Stefan de Kraker]

It want to be:
suspend inline fun <reified T> map

[Landry Norris]

That looks right. The body method uses a reified T, and since your T is not reified, it can't use it.

[Stefan de Kraker]

I want to make map a HttpResponse that is returned from my ktor.request method:

val response = ktor.request(PokemonApi.getAllPokemon(BATCH_SIZE, batch * BATCH_SIZE))
val entity = responseMapper.map(response)

[Stefan de Kraker]

but now responseMapper.map(response) is not allowed:
Not enough information to infer type variable T

[Landry Norris]

It doesn't know what type 'entity' should be. Either specify a type on entity or use brackets in map and specify a type.

[Landry Norris]

val entity: Result<PokemonList> = ...

Or

val entity = mapper.map<PokemonList>(response)

[Stefan de Kraker]

Is their a way that just does: ResponseMapper.map(response)?

[Landry Norris]

How would it know what the type is? You can specify the type of entity as in my first example (replace the ... with your response mapper).

[Stefan de Kraker]

We normally use Retrofit and the ResponseMapper looked like this:

fun <T> map(response: Response<T>): Result<T> = when {
    response.isSuccessful -> response.body()?.let(Result.Companion::success) ?: Result.failure(
        exception = Throwable("Http body is empty. HttpMessage: ${response.message()} HttpCode: ${response.code()}")
    )
    response.code() == 401 -> Result.failure(
        exception = AuthException()
    )
    else -> Result.failure(
        BackendException(
            errorCode = response.code()
        )
    )
}

[Landry Norris]

That code gets the type from the retrofit Response<T>.

[Stefan de Kraker]

Is that possible to do with Ktor?

[Landry Norris]

If you have a Response<T> in your old code, then T is known in the scope where you create the response. You'll want to just specify the type for your mapper instead.

[Landry Norris]

Alternatively, if you're set on matching retrofit, I haven't used it, but ktorfit exists. It's supposed to be like retrofit, but using ktor, and thus cross-platform.