Gang of Four · Visual Reference

Design Patterns

Animated structure diagrams, C++ examples, and real-world usage in simulators, compilers, and systems software.

Behavioral

Observer

One state change, many listeners notified automatically.

Swap algorithms at runtime without changing the caller.

Wrap requests as objects — queue, log, and undo them.

Add operations to objects without modifying their classes.

Creational

Let subclasses decide which class to instantiate.

Construct complex objects step by step.

Exactly one instance, globally accessible.

Structural

Wrap an object to add behavior without subclassing.

Make incompatible interfaces work together.

One clean interface over a complex subsystem.