Should I be able to @Provide a `List` ? e.g. ```...

# dagger

[Colton Idle]

Should I be able to @Provide a List ?

e.g.

@Provides
fun provideRetrofit(interceptors: List<Interceptor>): MyApiService {
    return MyRetrofitServiceBuilder().build(interceptors, "http://...")
}

@Provides
fun provideInterceptorList(@ApplicationContext context: Context): List<Interceptor> {
....

getting an error though.

error: [Dagger/MissingBinding] java.util.List<? extends okhttp3.Interceptor> cannot be provided without an @Provides-annotated method.
  public abstract static class SingletonC implements RollerToasterApplication_GeneratedInjector,

Using an ArrayList instead works, but just curious if I'm missing something basic here.

[ephemient]

because immutable List<out T> is declared as covariant in the type parameter, Kotlin translates List<Interceptor> to List<? extends Interceptor> in Java, which is different than List<Interceptor> in Java

[ephemient]

MutableList<T> is invariant, so it translates to List<T>

[ephemient]

but there is an annotation, List<@JvmSuppressWildcards T> explicitly for this purpose

[Colton Idle]

Oh shit. Wait. So what's the "proper" way forward? Use mutableList or the annotation route?

[ephemient]

check https://medium.com/androiddevelopers/dagger-in-kotlin-gotchas-and-optimizations-7446d8dfd7dc for this and other things to watch out for

[ephemient]

either way works, I'd go with @JvmSuppressWildcards as it better matches the intention

[Amanjeet Singh]

You can also use @IntoSet dagger multibindings if I am not wrong and provide a set collection instead if order not matters

[Colton Idle]

Order matters in this case because I'm using interceptors, but overall I was just curious why I can't Provide a List. Makes sense though.

For my final solution I just did this

@Provides
fun provideRetrofit(interceptors: @JvmSuppressWildcards List<Interceptor>): MyApiService {
    return MyRetrofitServiceBuilder().build(interceptors, "http://...")
}

I thought I would need @JvmSuppressWildcards on the provider return type itself, but I did not.

[FunkyMuse]

Just provide those interceptors into set using multi bindings, it's more convenient than a list

[Colton Idle]

I need a guaranteed order

[ephemient]

BTW, @IntoSet has the same issue with covariance at the consumer

[miqbaldc]

The same issues we found, but we’re using an Array instead of List

@Singleton
    @Provides
    fun provideSubmissionService(
        authenticator: Authenticator,
        interceptors: Array<out Interceptor>,
    ): SubmissionService =
        makeRetrofit(
            baseUrl = BuildConfig.BASE_SUBMISSION_URL,
            authenticator = authenticator,
            interceptors = interceptors,
        ).create(
            SubmissionService::class.java
        )

    @Singleton
    @Provides
    fun provideInterceptors(
        @ApplicationContext context: Context,
        cache: AccessTokenCache,
    ): Array<Interceptor> = arrayOf(
        ChuckerInterceptor(context),
        BearerTokenInterceptor(cache),
    )