DefaultBinding

Declares a default binding type for subtypes that use ContributesBinding, ContributesIntoSet, or ContributesIntoMap.

When a subtype has multiple supertypes and doesn't specify an explicit binding parameter, Metro normally requires one to disambiguate. With @DefaultBinding, the supertype can declare a default so subtypes don't have to.

The generic type T should be the default bound type, which the compiler plugin will read at compile-time.

@DefaultBinding<ThingFactory<*>>
interface ThingFactory<T : Thing> {
  fun create(): T
}

// Implicitly binds as ThingFactory<*> even though it has multiple supertypes
@ContributesBinding(AppScope::class)
@Inject
class MyFactory : ThingFactory<MyThing>, AnotherInterface

If multiple supertypes have @DefaultBinding, an explicit binding must be specified to disambiguate.

Abstract subtypes can supersede the parent default by specifying an explicit binding parameter on their contributing annotation.