Answer: 15

apps/typescript/15-function-overload/src/app/app.component.ts

@@ -8,7 +8,7 @@ import { createVehicle } from './vehicle.utils';
 export class AppComponent {
   car = createVehicle('car', 'diesel');
   moto = createVehicle('moto', 'diesel');
-  bus = createVehicle('bus', undefined, 20);
-  boat = createVehicle('boat', undefined, 300, true);
+  bus = createVehicle('bus', 20, true);
+  boat = createVehicle('boat', 300);
   bicycle = createVehicle('bicycle');
 }

apps/typescript/15-function-overload/src/app/vehicle.utils.ts

@@ -28,28 +28,70 @@ interface Boat {
 
 type Vehicle = Bicycle | Car | Moto | Bus | Boat;
 
+export function createVehicle(type: 'bicycle'): Bicycle;
+export function createVehicle(type: 'moto', fuel: Fuel): Moto;
+export function createVehicle(type: 'car', fuel: Fuel): Car;
+export function createVehicle(type: 'boat', capacity: number): Boat;
+export function createVehicle(
+  type: 'bus',
+  capacity: number,
+  isPublicTransport: boolean,
+): Bus;
 export function createVehicle(
   type: VehicleType,
-  fuel?: Fuel,
-  capacity?: number,
+  fuelOrCapacity?: Fuel | number,
   isPublicTransport?: boolean,
 ): Vehicle {
   switch (type) {
     case 'bicycle':
       return { type };
     case 'car':
     case 'moto':
-      if (!fuel) throw new Error(`fuel property is missing for type ${type}`);
-      return { fuel, type };
+      if (!fuelOrCapacity || typeof fuelOrCapacity === 'number') {
+        throw new Error(`fuel property is missing for type ${type}`);
+      }
+
+      return { fuel: fuelOrCapacity, type };
     case 'boat':
-      if (!capacity)
+      if (!fuelOrCapacity || typeof fuelOrCapacity === 'string') {
         throw new Error(`capacity property is missing for type boat`);
-      return { capacity, type };
+      }
+
+      return { capacity: fuelOrCapacity, type };
     case 'bus':
-      if (!capacity)
+      if (!fuelOrCapacity || typeof fuelOrCapacity === 'string') {
         throw new Error(`capacity property is missing for type bus`);
-      if (!isPublicTransport)
+      }
+      if (isPublicTransport === undefined) {
         throw new Error(`isPublicTransport property is missing for type bus`);
-      return { capacity, isPublicTransport, type };
+      }
+
+      return { capacity: fuelOrCapacity, isPublicTransport, type };
   }
 }
+
+// export function createVehicle(
+//   type: VehicleType,
+//   fuel?: Fuel,
+//   capacity?: number,
+//   isPublicTransport?: boolean,
+// ): Vehicle {
+//   switch (type) {
+//     case 'bicycle':
+//       return { type };
+//     case 'car':
+//     case 'moto':
+//       if (!fuel) throw new Error(`fuel property is missing for type ${type}`);
+//       return { fuel, type };
+//     case 'boat':
+//       if (!capacity)
+//         throw new Error(`capacity property is missing for type boat`);
+//       return { capacity, type };
+//     case 'bus':
+//       if (!capacity)
+//         throw new Error(`capacity property is missing for type bus`);
+//       if (!isPublicTransport)
+//         throw new Error(`isPublicTransport property is missing for type bus`);
+//       return { capacity, isPublicTransport, type };
+//   }
+// }