Is it possible to put createEffect() inside functions?

[Selol]

Hello there, I'm new to rxjs and ngrx and I have some codes works, and I found that everyone writes "createEffect" at the property area of a Class and I thought it should also work if I wrote it inside a function, and it turned out I was wrong. Can anybody help me to understand what's the magic here?

Working Code:

@Injectable()
export class UserEffects {
  loadUser$ = createEffect(() => this.actions$.pipe(
    ofType(getUser),
    first(),
    mergeMap(() => {
      return this.userService.getUser()
        .pipe(
          map(user => retievedUser({ user })),
          catchError(() => EMPTY)
        )
    })
  )
  );

  constructor(
    private actions$: Actions,
    private userService: UserService
  ) {
  }
}

Non-Working code:

@Injectable()
export class UserEffects {
  constructor(
    private actions$: Actions,
    private userService: UserService
  ) {
    createEffect(() => this.actions$.pipe(
      ofType(getUser),
      first(),
      mergeMap(() => {
        return this.userService.getUser()
          .pipe(
            map(user => retievedUser({ user })),
            catchError(() => EMPTY)
          )
      })
    )
    );
  }
}

I tried to learn https://github.com/ngrx/platform/blob/master/modules/effects/src/effect_creator.ts but I can't find anything special.
Thank you very much

[timdeschryver]

For now, effects can only be registered when they're assigned to a property.
Keep an eye out for #3669, which adds functional effects.