feat(structures): apply typeguards

Author: AsadHumayun

packages/structures/src/presences/activities/ActivityParty.ts

@@ -38,7 +38,7 @@ export class ActivityParty<Omitted extends keyof GatewayActivityParty | '' = ''>
 	 * The current size of the party
 	 */
 	public get currentSize() {
-		const array = this[kData].size as number[];
+		const array = this[kData].size;
 
 		return array ? (isArrayFieldSet(array, 0, 'number') ? array[0] : null) : null;
 	}
@@ -47,7 +47,7 @@ export class ActivityParty<Omitted extends keyof GatewayActivityParty | '' = ''>
 	 * The maximum size of the party
 	 */
 	public get maximumSize() {
-		const array = this[kData].size as number[];
+		const array = this[kData].size;
 
 		return array ? (isArrayFieldSet(array, 1, 'number') ? array[1] : null) : null;
 	}

packages/structures/src/utils/type-guards.ts

@@ -40,7 +40,11 @@ export function isFieldSet<Value extends object, Key extends string, Type extend
  * @param targetIndex - The target index of the element whose type to narrow
  * @param type - The type to compare against
  */
-export function isArrayFieldSet(array: unknown[], targetIndex: number, type: TypeofType): boolean {
+export function isArrayFieldSet<Type extends TypeofType, Index extends number>(
+	array: unknown,
+	targetIndex: Index,
+	type: Type,
+): array is Record<Index, Type> & unknown[] {
 	return Array.isArray(array)
 		? array.length >= targetIndex
 			? // eslint-disable-next-line valid-typeof