Adapter

Structural design patterns deal with inheritance and composition.
An adapter¹ is an object that converts the interface of one object to one that another can understand.
- Example: A XML to JSON parser
- Implements the interface of one object and wraps the other (to hide complexity)

flowchart TD
 A(Client)
 B(Client Interface)
 C(Adapter)
 D(Service)

 A --> B
 C -.-> B
 C -.-> D

An object adapter works with the client interface
A class adapter implements the interface of the client and service classes.
When to use?
1. An existing class' interface isn't compatible with the rest of a system's code.
2. Reuse existing subclasses that don't have common functionality.
Implementation
1. Write client interface to describe interaction between client and service.
2. Adapter class should have a reference to the service. The service handles the business logic.
Follows Single Responsibility Principle and Open/Closed Principle.
However, sometimes its just easier to make the service compatible with the rest of your code.