Dagger/Hilt is there a difference in modules if they are abstract classes or interfaces?

Question

I have a question and maybe someone with experience can make things a little more clear for me. I have written Hilt modules both as interfaces or as abstract classes. Is there an actual difference between those two? For example, I have changed the following module in Hilt on my app and it still working.

@Module
@InstallIn(ViewModelComponent::class)
abstract class LocalModules {

    @Binds
    @ViewModelScoped
    abstract fun bindTemporaryImageFileFactory(factory: TemporaryImageFileFactoryImpl): TemporaryImageFileFactory

}

or

@Module
@InstallIn(ViewModelComponent::class)
interface LocalModules {

    @Binds
    @ViewModelScoped
    fun bindTemporaryImageFileFactory(factory: TemporaryImageFileFactoryImpl): TemporaryImageFileFactory
}

Answer 1

There is no difference between using interface or abstract class when @Binds is used. These @Module classes' @Binds methods are used by Dagger only to understand which implementation class (TemporaryImageFileFactoryImpl) should be linked to the interface (TemporaryImageFileFactory).

Using this information, Dagger generates its own code to link the interface with the implementation. After successful build, in IDE you can see that no matter what you use, the @Binds method will show as unused.