immer-example.ts

@State<AnimalsStateModel>({
    name: 'animals',
    defaults: {
        zebra: {
            food: [],
            name: 'zebra'
        },
        panda: {
            food: [],
            name: 'panda'
        }
    }
})
export class AnimalState {
    
    @Mutation()
    @Action(FeedZebra)
    public feedZebra(ctx: StateContext<AnimalsStateModel>, { payload }: FeedZebra): AnimalsStateModel {
        ctx.setState((state: AnimalsStateModel) => { // immutable mutation with immer (analogue produce)
          state.zebra.food.push(payload);
          return state;
        })
    }
  
}