#Strategy

#Overview

Define a family of algorithms and make them interchangeable.

#When to use

• You need runtime selection of behavior.
• You want to avoid large switch statements.

#Java example

interface PricingStrategy {
    int price(int base);
}

class DiscountStrategy implements PricingStrategy {
    public int price(int base) { return base - 10; }
}

class PricingService {
    private PricingStrategy strategy;
    PricingService(PricingStrategy strategy) { this.strategy = strategy; }
    int compute(int base) { return strategy.price(base); }
}

#TypeScript example

type PricingStrategy = (base: number) => number;

const discount: PricingStrategy = (base) => base - 10;

class PricingService {
  constructor(private strategy: PricingStrategy) {}
  compute(base: number): number { return this.strategy(base); }
}

#Pros and cons

Pros:

• Replaces complex conditional logic.
• Easy to add new strategies.

Cons:

• More classes or functions to manage.
• Clients must choose a strategy.

#Common pitfalls

• Strategies with overlapping responsibilities.
• Hard-coded strategy selection in many places.

#Related patterns

• State
• Decorator