ngrx-effects-runtime.ts

@Injectable()
export class TodosEffects {
  @Effect()
  public setTodos$ = this.actions$.pipe(
    ofType(Actions.GET_TODOS),
    exhaustMap(() => someService.getTodos()),
    map((todos) => ({
      type: Actions.SET_TODOS,
      payload: todos
    }))
  );

  constructor(private actions$: Actions) {}
}

// В рантайме после вызова декораторов

class TodosEffects {
  public static '__@ngrx/effects__' = [
    {
      propertyName: 'setTodos$',
      dispatch: true
    }
  ];

  public setTodos$ = ...
}