function Init(obj: { [key: string]: any }, Class: any) {
  return function(target: any, name: string) {
    Object.defineProperty(target, name, {
      get: () => {
        return new Class(obj[name]);
      },
    });
  };
}

class Item {
  item: IItem;
  associatedItems: Item[];

  constructor(item: IItem, ...associatedItems: Item[]) {
    this.item = item;
    this.associatedItems = associatedItems;
  }

  doSomething() {
    return true;
  }
}

interface IItem {
  some: string;
}

const items: { [K in keyof Items]: IItem } = {
  AIR_PODS: {
    some: 'key',
  },
  BOSE_SPEAKER: {
    some: 'thiing',
  },
};

class Items {
  @Init(items, Item)
  AIR_PODS: Item;
  BOSE_SPEAKER: Item;
}

const thing = new Items();

console.log(thing.AIR_PODS.doSomething());