Modellierung diskriminierter Zustands-Union-Typen mit reaktiven Signals

import { Injectable, signal, computed } from '@angular/core';
 
type FetchStatus =
  | { state: 'idle' }
  | { state: 'loading' }
  | { state: 'success'; data: string[] }
  | { state: 'error'; message: string };
 
@Injectable({ providedIn: 'root' })
export class DataStateStore {
  private readonly statusSignal = signal<FetchStatus>({ state: 'idle' });
 
  readonly isLoaded = computed(() => this.statusSignal().state === 'success');
  readonly currentPayload = computed(() => {
    const s = this.statusSignal();
    return s.state === 'success' ? s.data : [];
  });
 
  setSuccess(payload: string[]): void {
    this.statusSignal.set({ state: 'success', data: payload });
  }
}