Strategy AKA Policy Dale Willey Ian Price

Overview Definitions Difference between Strategy pattern and strategy Where would you use this? Challenges

Definitions (Metsker) Encapsulate alternative strategies, or approaches, in separate classes that each implement a common operation. (GoF) Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently form clients that use it.

What That Really means... Multiple functions that take the same arguments and return something of the same type.

Strategy Pattern vs strategy strategy is a single way of doing things Strategy Pattern is applying different strategies Discussion?

Questions so far...

Example: Playing Monopoly How could the strategy pattern be applied here? What different strategies are there?

President’s Cabinet In the context of the President’s advisors, how could the strategy pattern be applied here? What different strategies are there?

VCR Does a VCR implement a strategy pattern with respect to playing tapes? With setting the clock? A single VCR? All VCRs?

Challenges Reexamine the definitions... (Metsker) Encapsulate alternative strategies, or approaches, in separate classes that each implement a common operation. (GoF) Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently form clients that use it. What kind of relationship are they describing? 1-1? 1-∞?

Challenges (cont) How is this like Chain of Responsibility?

Challenges (cont cont) Are business contingency plans Chains of Responsibility or Strategies?

Challenges (cont cont cont) Is a random Chain of Responsibility a Strategy?

Challenges (still cont) Is a completely predictable way of applying strategies a Strategy pattern? Is maxing the bet every time in poker (constantly bluffing) an example of a Strategy pattern?

Review Strategy Pattern uses 1 to n strategies in a modular way The point to the Strategy Pattern is in having and using strategies rather than emphasis on the selection method