PatternKit.Examples 0.8.2

PatternKit

Fluent Design Patterns for Modern .NET
Elegant, declarative, allocation-light implementations of classic patterns—optimized for .NET 9.

✨ Overview

PatternKit is a modern library that reimagines the GoF design patterns for .NET 9+.
Instead of boilerplate-heavy class hierarchies, we favor:

• Fluent builders and DSLs (chainable, declarative, composable).
• Source generators to eliminate reflection and runtime overhead.
• Zero-allocation hot paths for performance-critical scenarios.
• Strong typing with in parameters, avoiding boxing and defensive copies.
• Testable, deterministic APIs that pair naturally with BDD and xUnit/NUnit/MSTest.

Our goal: make patterns a joy to use, not a chore to implement.

🚀 Quick Start

Install via NuGet:

dotnet add package PatternKit --version <latest>

Use a pattern immediately—here’s a simple Strategy:

using PatternKit.Behavioral.Strategy;

var classify = Strategy<int, string>.Create()
    .When(i => i > 0).Then(i => "positive")
    .When(i => i < 0).Then(i => "negative")
    .Default(_ => "zero")
    .Build();

Console.WriteLine(classify.Execute(5));   // positive
Console.WriteLine(classify.Execute(-3));  // negative
Console.WriteLine(classify.Execute(0));   // zero

Or a TryStrategy for first-match-wins pipelines:

var parse = TryStrategy<string, int>.Create()
    .Always((in string s, out int r) => int.TryParse(s, out r))
    .Finally((in string _, out int r) => { r = 0; return true; })
    .Build();

if (parse.Execute("123", out var n))
    Console.WriteLine(n); // 123

📦 Patterns (Planned & In Progress)

PatternKit will grow to cover Creational, Structural, and Behavioral patterns with fluent, discoverable APIs:

Each pattern will ship with:

• A fluent API (.When(...), .Then(...), .Finally(...), etc.)
• Source-generated boilerplate where possible.
• DocFX-ready documentation and TinyBDD tests.

🧪 Testing Philosophy

All patterns are validated with TinyBDD and xUnit:

[Feature("Strategy")]
public class StrategyTests : TinyBddXunitBase
{
    [Scenario("Positive/negative classification")]
    [Fact]
    public async Task ClassificationWorks()
    {
        await Given("a strategy with three branches", BuildStrategy)
            .When("executing with 5", s => s.Execute(5))
            .Then("result should be 'positive'", r => r == "positive")
            .AssertPassed();
    }
}

We keep tests behavior-driven, readable, and high coverage.

💡 Design Goals

• Declarative: Favor expression-based and fluent APIs over imperative setup.
• Minimalism: Prefer single-responsibility types and low ceremony.
• Performance: Allocation-free handlers, in parameters, ahead-of-time friendly.
• Discoverability: IntelliSense-first APIs; easy to read, easy to write.
• Testability: TinyBDD integration and mocks built-in where applicable.

🛠 Requirements

• .NET 9.0 or later (we use in parameters and modern generic features).
• C# 12 features enabled (readonly struct, static lambdas, etc.).

📚 Documentation

Full API documentation is published with DocFX (coming soon). Each type and member ships with XML docs, examples, and cross-links between patterns.

🤝 Contributing

We welcome issues, discussions, and PRs. Focus areas:

• Adding new patterns (start with Behavioral for max impact)
• Improving fluent builder syntax and source generator coverage
• Writing TinyBDD test scenarios for edge cases

📄 License

MIT — see LICENSE for details.

❤️ Inspiration

PatternKit is inspired by:

• The Gang of Four design patterns
• Fluent APIs from ASP.NET Core, System.Linq, and modern libraries
• The desire to make patterns readable, performant, and fun to use in 2025+