Duplicate Interfaces

The Problem

export interface INotificationService {
  sendNotification(message: string, recipient: string): Promise<void>;
}

// Multiple implementations of the same interface
export class EmailNotificationService implements INotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

export class SmsNotificationService implements INotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

export class PushNotificationService implements INotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

The Problem: When resolving INotificationService, which implementation should the container use?

Detection

❌ Error: Interface 'INotificationService' is implemented by multiple classes:
  - EmailNotificationService (/path/to/services/EmailNotificationService.ts)
  - SmsNotificationService (/path/to/services/SmsNotificationService.ts)
  - PushNotificationService (/path/to/services/PushNotificationService.ts)

Multiple classes implement the same interface(s): INotificationService.
Each interface should only be implemented by one class for proper dependency injection.

How to Fix

Create specific interfaces:

// Base interface
export interface INotificationService {
  sendNotification(message: string, recipient: string): Promise<void>;
}

// Specific interfaces
export interface IEmailNotificationService extends INotificationService {}
export interface ISmsNotificationService extends INotificationService {}
export interface IPushNotificationService extends INotificationService {}

// Implementations
export class EmailNotificationService implements IEmailNotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

export class SmsNotificationService implements ISmsNotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

export class PushNotificationService implements IPushNotificationService {
  async sendNotification(message: string, recipient: string) { /* ... */ }
}

Usage:

import { container } from './container.gen';

// ✅ Each interface has one implementation - no ambiguity!
const emailService = container.resolve('IEmailNotificationService');
const smsService = container.resolve('ISmsNotificationService');
const pushService = container.resolve('IPushNotificationService');