feat(core): use Object.Paths in byDeep method of TrackByService

npm/ng-packs/packages/core/src/lib/services/track-by.service.ts

@@ -1,18 +1,19 @@
 import { Injectable, TrackByFunction } from '@angular/core';
+import { O } from 'ts-toolbelt';
 
 @Injectable({
   providedIn: 'root',
 })
 export class TrackByService<ItemType = any> {
   by<T = ItemType>(key: keyof T): TrackByFunction<T> {
-    return ({}, item) => item[key];
+    return (_, item) => item[key];
   }
 
-  byDeep<T = ItemType>(...keys: (string | number)[]): TrackByFunction<T> {
-    return ({}, item) => keys.reduce((acc, key) => acc[key], item);
+  byDeep<T = ItemType>(...keys: T extends object ? O.Paths<T> : never): TrackByFunction<T> {
+    return (_, item) => keys.reduce((acc, key) => acc[key], item);
   }
 
   bySelf<T = ItemType>(): TrackByFunction<T> {
-    return ({}, item) => item;
+    return (_, item) => item;
   }
 }

npm/ng-packs/packages/core/src/lib/tests/track-by.service.spec.ts

@@ -11,17 +11,11 @@ describe('TrackByService', () => {
 
   describe('#byDeep', () => {
     it('should return a function which tracks a deeply-nested property', () => {
-      expect(
-        service.byDeep(
-          'a',
-          'b',
-          'c',
-          1,
-          'x',
-        )(284, {
-          a: { b: { c: [{ x: 1035 }, { x: 1036 }, { x: 1037 }] } },
-        }),
-      ).toBe(1036);
+      const obj = {
+        a: { b: { c: { x: 1036 } } },
+      };
+
+      expect(service.byDeep<typeof obj>('a', 'b', 'c', 'x')(284, obj)).toBe(1036);
     });
   });