# Design Patterns
## Creation
- Builder: hide complexity in object creation
- Factory: can produce many types
- Prototype: partial or complete object that can be used/cloned
- Singleton: only one, cannot be cloned

## Structural
- Adapter: adapts interface X to work with Y
- Bridge: decoupling class/interface from implementation (frequency changes)
- Composite: treat single and composite objects uniformly
- Decorator: add behaviour of object without modifying class
- Facade: simplified wrapping api surrounding complex code
- Flyweight: reduce memory usage by storing data that can be reused externally
- Null object: No-op object used to satisfy dependency when no-op desired
- Proxy: class which acts as an interface to a resource

## Behavioural
- Chain of responsibility: chain of components that each get a chance to act
- Command: object representing one instruction
- Interpreter: interprets structured text and parses it into symbols/tokens
- Iterator: facilitates traversal of data structure
- Mediator: allows communication of components that need not be aware of one another
- Memento: handle representing state - sometimes used for rollback
- Observer: object which is informed of events often through callback function
- Strategy: enabling behaviours to be selected at runtime or compile time
- Visitor: can traverse inheritance hierarchies