Design patterns describe recurring solutions to common problems in object-oriented software design. Patterns are categorized into three types:

• Creational: design patterns that deal with object-creation mechanisms, trying to create objects in a manner suitable to the situation.
• Structural: design patterns that ease the design by identifying a simple way to realize relationships between entities.
• Behavioral: design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.

This section introduces some OOP design patterns on a very high level, as well as the FP counterparts:

• Strategy
• Command
• Observer
• Proxy
• Visitor