ExampleQualifier.kt

// For example, we have an interface called LoggerSource. 
// It has two separate implementations: 
// InMemoryLogger & DatabaseLogger
@Qualifier
annotation class InMemoryLogger

@Qualifier
annotation class DatabaseLogger

// When creating the `LoggerModule`, we can define 
// two abstract methods for both the implementations
// and add the appropriate @qualifiers for each method.
@InstallIn(SingletonComponent::class)
@Module
abstract class LoggerModule {
    
    @DatabaseLogger
    @Binds
    abstract fun bindDatabaseLogger(impl: LoggerLocalDataSource): LoggerSource
  
    @InMemoryLogger
    @Binds
    abstract fun bindInMemoryLogger(impl: LoggerInMemoryDataSource): LoggerSource
}


// When injecting the interface in MainActivity, 
// we can specify which implementation we want to inject
// using the qualifier name
@AndroidEntryPoint
class MainActivity : AppCompatActivity() { 
  
  @DatabaseLogger
  @Inject 
  lateinit var logger: LoggerSource
}