Class-level multi-bindings

From what I understand, multi-bindings must currently be defined in a component. From the README:

@Component
abstract class MyComponent {
    abstract val fooMap: Map<String, Foo>

    @IntoMap
    @Provides
    protected fun provideFoo1(): Pair<String, Foo> = "1" to Foo("1")

    @IntoMap
    @Provides
    protected fun provideFoo2(): Pair<String, Foo> = "2" to Foo("2")
}

It would be great if instead, the @IntoMap and @IntoSet annotations could be applied to an injectable class. Anvil allows this kind of syntax:

@ContributesMultibinding(Scope::class, boundType = Foo::class)
@StringKey("my-first-foo")
class Bar @Inject constructor() : Foo {}

@ContributesMultibinding(Scope::class, boundType = Foo::class)
@StringKey("my-second-foo")
class Baz @Inject constructor() : Foo {}

And the component would as a result contain a Map<String, Foo>, itself containing {"my-first-foo": Bar(), "my-second-foo": Baz()}

This helps with composition, as adding an entry to the set/map only requires defining a type (or adding a dependency), no changes are needed to the component code itself.

[evant]

In fact I don’t think there’s anything blocking someone making an ‘anvil’ for kotlin-inject right now, it should already support multiple rounds properly. You would just be generating the @Component classes based on your annotations. If anyone want’s to take a stab at it I’d be glad to answer any questions/fix an issues related to it.

[evant]

Note that Hilt is implemented in much the same way as Anvil as a separate code generator, really the only difference is that it’s first-party in dagger where anvil is not. I will make no promises on future additions like this but if I where to do something first-party it would probably follow the same pattern. In the meantime, I’d fully support any project built on top of this that implemented some or all of anvil’s feature-set. Extensibility is a goal and I think it’s a good way to allow experimentation and more complex use-cases without complicating the core library.