Why the dagger graph works works in java but in Kotlin it says missing Provides when I have provided?

Question

I have some issues when converting dagger interfaces from java to Kotlin

I got [Dagger/MissingBinding] java.util.Map cannot be provided without an @Provides-annotated method.

Here is my interface

   interface TopicConfigModule {
    @Binds
    @IntoMap
    @StringKey(NAME)
    fun bindCommandHandler(handler: TopicCommandHandler): CommandHandler

    companion object {
        @JvmStatic
        @Provides
        @FragmentScope
        fun provideHubsConfig(
            commandRegistry: Map<String, CommandHandler>
        ): Config {
            return ...
        }
    }
}

and CommandHandler is java interface

public interface HubsCommandHandler {```}

try to use commandRegistry: Map<String, @JvmSuppressWildcards CommandHandler>, also you don't need @JvmStatic (I assume that you're using dagger 2.26 or higher) — IR42
@IR42 It works but I, am not sure why we need JvmSuppressWildcards . And please write down as answer I will vote for your answer. — I.S

IR42 IR42 · Accepted Answer · 2020-05-04T19:21:31

Map in Kotlin is covariant (variance) on its value type (public interface Map<K, out V>), but Map in Java is not. Your function will be translated to

Config provideHubsConfig(Map<String, ? extends CommandHandler> commandRegistry) { ... }

but dagger provides exactly Map<String, CommandHandler>. So we need to suppress wildcards with @JvmSuppressWildcards

commandRegistry: Map<String, @JvmSuppressWildcards CommandHandler>

Calling Kotlin from Java - variant-generics

Why the dagger graph works works in java but in Kotlin it says missing Provides when I have provided?

1 Answers