// preferred way, multi provider concept:
providers: [
  {
    provide: HOOK_ACTION_BAR,
    useValue: [{ template: SomeComponent, priority: 10, placement: 'left' } as ActionBarItem],
    multi: true
  }
]

// use services:
this.actionBarService.add({ template: SomeComponent, priority: 10, placement: 'left' });