Structural patterns

Wrap an incompatible API behind the interface your application already expects so the rest of the code stays unchanged.

Separate an abstraction from its implementation so both sides can vary independently without multiplying concrete types.

Treat individual objects and object groups uniformly so recursive tree structures stay simple to traverse and aggregate.

Add behavior around an object dynamically by wrapping it with small focused layers that share the same interface.

Provide one simplified entry point over several collaborating subsystems so callers can trigger a workflow without knowing every step.

Share intrinsic immutable state across many small objects so large collections stay cheaper in memory and easier to manage.

Control access to another object by standing in front of it to add caching, authorization, rate limiting, or lazy loading.