Strategy design pattern

What is Strategy design pattern?

• It is behavioural design pattern. This pattern is also referred as Policy pattern.
• This pattern lets us define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
• This pattern is useful to when there are different algorithms to choose at runtime depending upon user selection/context.
• Same behaviour(end result) however different ways to achieve it.

Real world analogy:

• Consider example of project management.
• To achieve this, there are different strategies/methodologies to choose from. However, main behaviour/end goal is better project management.
• There could be various strategies like Scrum, Kanban, Lean,Waterfall and many more.

Example in software/apps development:

• Consider scenario of Payment processing within mobile application.
• We can infer that there is one behaviour payment that needs to be achieved. However, there are multiple ways/payment mechanisms to complete payment.
• For example, payment can be done using CreditCard , DebitCard or any other mobile wallet APIs. Ultimate goal is to pay specific amount in a specified currency.
• Sample code in swift: https://github.com/ParthContractor/StrategyDesignPattern

Benefits:

• More isolated, understandable and readable code.
• Adherence to Open/Closed principle.
• Changing algorithms/strategies at runtime is easy.

Drawbacks:

• There could be possibility of increased distinct strategies over the period of time and apparently cumbersome to handle/manage them all.
• Clients must understand all strategies to properly utilised one over another at runtime.

Comparison with Template method pattern:

• Template method depends upon single algorithm in abstract super class and allowing concrete subclasses to override part of steps.
• However, Strategy design pattern enables selection of algorithm at runtime. Different strategy is applied to object at runtime to achieve its specific behaviour.

Other interesting articles/reference materials:

• https://sourcemaking.com/design_patterns/strategy
• https://refactoring.guru/design-patterns/strategy
• https://en.wikipedia.org/wiki/Strategy_pattern
• https://stackoverflow.com/questions/31608902/polymorphism-vs-strategy-pattern

Summary:

Strategy pattern is useful when you want to decide during run time how you want to run a particular behaviour from set predefined ways.