Serialize Map in Kotlin about moshi HOT 12 CLOSED

You don't need Kotlin to reproduce it. Here's a minimal failing example in Java:

class Dao {
    Map<String, ? extends String> map;
}

public class MoshiTest {
    @Test
    public void testMoshi() throws Exception {
        new Moshi.Builder().build().adapter(Dao.class);
    }
}

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Yup. For strings this is easy. But when the wildcard really means something, we're in trouble. For example, how would we decode this?

Map<String, ? extends Object>

Would we use the base type? That's a bit weird because it'll be asymmetrical. I might be overthinking this.

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Maybe we can have a specific use case for simple types like Primitives and Strings

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Or final types.

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By the way it's exactly the same beaviour for all Generics in kotlin. For instance, For List<Something> it will generate List<? extends Something>.
In addition when we register an adapter class for Something, moshi ignores it because it looks for an adapter for ? extends Something

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@swankjesse Maybe you want me to create another issue to fit the need better ?

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I stumbled upon the same issue when using kotlin's wildcard collections
I really like what @cypressious suggests, what about treating wildcards such as ? extends FinalType as FinalType?

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and if I would implement that, would it be sensible to put that into Types.equals?

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in the meantime I'm using this workaround, maybe it'll help someone:

inline fun <reified T : Any> Moshi.Builder.addWithSubtypes(adapter: JsonAdapter<T>): Moshi.Builder =
    add(object : JsonAdapter.Factory {
      val subtype = Types.subtypeOf(T::class.java)

      override fun create(type: Type?,
                          annotations: MutableSet<out Annotation>?,
                          moshi: Moshi?): JsonAdapter<T>? =
          when (type) {
            T::class.java, subtype -> adapter
            else                   -> null
          }
    })

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@adelnizamutdinov nice! Yeah, I think we probably just want to treat ? extends Type as Type. I don’t think it’s reasonable to look at the final/nonfinal attribute of the class because that’s often an implementation detail. (Think of Guava’s ImmutableList, which is non-final).

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I think Kotlin has relaxed the wildcard emission in class files in later betas of 1.0. I'll check today.

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This works in Kotlin 1.0 or newer

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