Patterns

Welcome! This section is the reference home for PatternKit’s core building blocks. Each page explains the why, the shape (APIs), and gives a tiny snippet so you can drop the pattern straight into your codebase.

If you’re looking for end-to-end, production-shaped demos, check the Examples & Demos section—those pages show these patterns working together (auth/logging chains, payment pipelines, router, coercer, etc.).

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How these fit together

• Behavioral patterns describe what runs & when (chains and strategies, observers, mediators, state machines).

• Creational helpers build immutable, fast artifacts (routers, pipelines) from tiny delegates.

• Common themes:

  • First-match wins (predictable branching without if ladders).
  • Branchless rule packs (ActionChain<T> with When/ThenContinue/ThenStop/Finally).
  • Immutable after Build() (thread-safe, allocation-light hot paths).

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Behavioral

Chain

• Behavioral.Chain.ActionChain Compose linear rule packs with explicit continue/stop semantics and an always-runs Finally.

• Behavioral.Chain.ResultChain Like ActionChain, but each step returns a result; first failure short-circuits.

Strategy

• Behavioral.Strategy.Strategy Simple strategy selection—pick exactly one handler.

• Behavioral.Strategy.TryStrategy First-success wins: chain of Try(in, out) handlers; great for parsing/coercion.

• Behavioral.Strategy.ActionStrategy Fire one or more actions (no result value) based on predicates.

• Behavioral.Strategy.AsyncStrategy Async sibling for strategies that await external work.

Template

• Behavioral.Template.TemplateMethod Abstract base with OnBefore/Step/OnAfter hooks and optional synchronization.

• Behavioral.Template.Template (Fluent) Fluent, allocation-light template with multicast hooks and TryExecute.

• Behavioral.Template.AsyncTemplate (Fluent) Async fluent sibling with cancellation-aware hooks and TryExecuteAsync.

Iterator

• Behavioral.Iterator.ReplayableSequence
  Forkable, lookahead, on-demand buffered sequence with immutable struct cursors, speculative forks, and LINQ interop (pay-as-you-go buffering).
• Behavioral.Iterator.WindowSequence
  Sliding / striding window iterator with optional partial trailing window and buffer reuse for zero-allocation full windows.

Mediator

• Behavioral.Mediator.Mediator

Command

• Behavioral.Command.Command

Observer

• Behavioral.Observer.Observer
• Behavioral.Observer.AsyncObserver

State

• Behavioral.State.StateMachine Fluent, generic state machine with entry/exit hooks and transition effects; immutable after Build().

Interpreter

• Behavioral.Interpreter.Interpreter Parse and evaluate domain-specific languages with composable expression trees.

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Creational (Builder)

• Creational.AbstractFactory Family-aware factory that produces related objects with consistent themes.

• Creational.Builder.BranchBuilder Zero-if router: register (predicate → step) pairs; emits a tight first-match loop.

• Creational.Builder.ChainBuilder Small helper to accumulate steps, then project into your own pipeline type.

• Creational.Builder.Composer Compose multiple builders/artifacts into a single product.

• Creational.Builder.MutableBuilder A lightweight base for fluent, mutable configuration objects.

• Creational.Factory Key → creator mapping with optional default; immutable and allocation-light.

• Creational.Prototype Clone-and-tweak via fluent builders and keyed registries.

• Creational.Singleton Fluent, thread-safe singleton with lazy/eager modes and init hooks.

Structural

• Structural.Adapter.Adapter Fluent in-place mapping with ordered validation for DTO projection.

• Structural.Bridge.Bridge Abstraction/implementation split with fluent pre/post hooks and validations.

• Structural.Composite.Composite Uniform treatment of leaves and compositions via seed+combine folding.

• Structural.Decorator.Decorator Fluent wrapping with before/after/around hooks and composition.

• Structural.Facade.Facade Unified subsystem interface with named operations.

• Structural.Flyweight Identity sharing for high-volume immutable instances.

• Structural.Proxy Virtual/protection/logging/caching/remote proxies.

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Additional Patterns

• TypeDispatcher Type-safe runtime dispatch that routes objects to handlers based on their concrete type.

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Where to see them in action

• Auth & Logging Chain — request-ID logging + strict auth short-circuit using ActionChain.
• Strategy-Based Coercion — TryStrategy turns mixed inputs into typed values.
• Mediated / Config-Driven Transaction Pipelines — chains + strategies for totals, rounding, tender routing.
• Minimal Web Request Router — BranchBuilder for middleware and routes.
• State Machine — order lifecycle with entry/exit hooks and default behaviors.

Tip: every pattern page has a tiny example; the demos show realistic combinations with TinyBDD tests you can read like specs.