Idea

• Core flow stays stable: “compute price,” “send notification,” “score risk.”
• Variations live in pluggable strategies (implements a small interface).

Step shape

abstract class PricingStrategy {
  double quote(double base);
}

class StandardPricing implements PricingStrategy {
  @override
  double quote(double base) => base;
}

class MemberPricing implements PricingStrategy {
  @override
  double quote(double base) => base * 0.9;
}

class Checkout {
  final PricingStrategy pricing;
  Checkout(this.pricing);

  double total(double base) => pricing.quote(base);
}

• New member tier? Add class VipPricing implements PricingStrategy instead of editing Checkout internals.

Practice tasks

• Replace a three-branch if on an enum with a Map<Role, PricingStrategy> or a small registry.
• Identify one switch that grows every sprint; sketch Strategy types for two branches only.
• Note when O is overkill: two branches that never grow can stay as if.