Decorator Pattern

Decorator Pattern

What is it?

Structural design pattern that allows the behaviour of objects to be enhanced placing them into special wrapper objects

What problems does it solve?

Altering behaviours to an object at runtime

Why not just use inheritance?

• Inheritance can only occur at compile time
• Most languages only allow single inheritance

Decorator Pattern

• ConcreteComponent and
  decorators all conform to an interface
• ConcreteComponent and ConcreteComponent that have been decorated can be treated in the same way
• Decorators hold an instance of the ConcreteComponent via composition

Decorator Pattern

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Current requirements:

Decorator Pattern

Updated requirements:

Decorator Pattern

Gotchas:

• Why is decorator pattern structural instead of behavioural?
  • conceptual - Why decorator is a structural and not behavioral design pattern? - Stack Overflow
• Difference between strategy and decorator pattern?
  • Strategy Pattern V/S Decorator Pattern - Stack Overflow