Strategy Pattern

Strategy Pattern Intent Also known as “Policy” Motivating example Define a family of algorithms, encapsulate each one,and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it. Also known as “Policy” Motivating example Different line break algorithms for varying types of text

SimUDuck example Joe works for a company that makes a highly successful duck pond simulation game, SimUDuck. The game can show a large variety of duck species swimming and making quacking sounds.

Inheritance based design

Inheritance based design Now RubberDuck can fly!

What about using Interface?

What about using Interface? Duplicated code! Now try changing fly().

Encapsulate Behaviors Separate them out of the client Define as interfaces

Delegate behaviors

Strategy Pattern

Design Principles Identify the aspects of your application that vary and separate them from what stays the same. Program to an interface, not an implementation. Favor composition over inheritance Has-A is better than Is-A

Strategy Pattern in FP Different strategies are just different functions Higher order functions (HOF) Function is first -class, can live alone and be passed around In OOP, method is not first-class, must be encapsulated in a class (“world of nouns”)

What about polymorphism? Dispatch on type Calling different functions according to the data type In Clojure Custom data type: defrecord Custom behavior groups (interface): defprotocol Don't support inheritance