Adapter

Translating between interfaces

Intent: convert the interface of an existing class into the interface your code expects, so they can work together without changing either. Typical uses: wrapping a third-party SDK behind your own interface, integrating a legacy module, or supporting several vendors (two payment providers, two SMS services) through one interface. The adapter translates method names, argument shapes, units (cents versus decimal amounts) and errors. Use it when you integrate code you do not control. A useful side effect is an anti-corruption layer: vendor types stay inside the adapter instead of leaking across your codebase. Avoid adapters that merely rename methods of code you own; change the code instead.

Wrap, extend and simplify

Structural patterns compose objects so interfaces fit together cleanly.

Adapting an SMS vendor SDK

The vendor client is hypothetical; your app sees only SmsSender.

// Our interface
interface SmsSender {
  send(phone: string, text: string): Promise<{ messageId: string }>;
}

// Shape of a (hypothetical) vendor SDK we cannot change
interface VendorSmsClient {
  messages: {
    create(params: { to: string; body: string; from: string }):
      Promise<{ sid: string; status: string }>;
  };
}

class VendorSmsAdapter implements SmsSender {
  constructor(private client: VendorSmsClient, private fromNumber: string) {}

  async send(phone: string, text: string) {
    try {
      const res = await this.client.messages.create({ to: phone, body: text, from: this.fromNumber });
      return { messageId: res.sid };
    } catch (err) {
      throw new SmsDeliveryError('Vendor rejected the message', { cause: err });
    }
  }
}

A travel plug adapter

A plug adapter lets your laptop charger fit a foreign socket without rewiring either the charger or the wall.

त्वरित जाँच: When is an Adapter the right choice?

• When integrating a third-party API whose interface differs from the one your code expects
• When you need exactly one instance of a class
• When you want to undo user actions
• When you need to build an object step by step