Behavioral Patterns

Overview

Behavioral patterns focus on communication and responsibility between objects. They help manage control flow and evolving business logic.

Common Behavioral Patterns

• Strategy
• Observer
• Command
• State
• Chain of Responsibility

sequenceDiagram
    participant Client
    participant Context
    participant StrategyA
    Client->>Context: execute(request)
    Context->>StrategyA: process(request)
    StrategyA-->>Context: result
    Context-->>Client: result

Practical Example - Strategy

public interface IDiscountStrategy
{
    decimal Apply(decimal total);
}

public sealed class LoyaltyDiscount : IDiscountStrategy
{
    public decimal Apply(decimal total) => total * 0.90m;
}

Different strategies are selected based on customer segment.

Production Guidance

• Use strategy for variable pricing and policy logic
• Use observer for domain events and notifications
• Use command for auditable operations and retries

Common Pitfalls

• Overusing observer without event ownership rules
• Hiding critical branching logic in too many small classes
• Forgetting idempotency for command retries

Key Takeaways

• Behavioral patterns separate decision logic from orchestration.
• Strategy and command patterns support safer business evolution.
• Event-driven behavior requires ownership and monitoring.