multi-check-option-1.ts

abstract class MultiCheckOption { }                        // (1)

@Component({
  selector: 'simple-check-option',
  providers: [
    {                                                      // (2)
      provide: MultiCheckOption,
      useExisting: SimpleCheckOptionComponent,
    }
  ]
})
export class SimpleCheckOptionComponent { ... }

@Component({
  selector: 'user-check-option',
  providers: [
    {                                                      // (3)
      provide: MultiCheckOption,
      useExisting: UserCheckOptionComponent
    }
  ]
})
export class UserCheckOptionComponent { ... }