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Nilay Vishwakarma edited this page Jun 6, 2025 · 7 revisions

What is SharpFsm?

A flexible finite state machine (FSM) library for .NET written in C#, it is designed to create and manage Finite State Machines (FSMs) in a simple and efficient way. It allows developers to define states, transitions, and events, enabling the modeling of complex behaviors in a structured manner.

Features

  • State Management: Easily define and manage states in your FSM. Strongly-typed FSMs using enums for states
  • Transition Handling: Transition conditions and side effects.
  • Serialization: Serialization to/from JSON and YAML.
  • Builder Pattern: Builder pattern for easy FSM construction.
  • Extensible: Easily extend the library to fit specific needs or integrate with other systems.
  • Cross-Platform: Multi-targeted for broad .NET compatibility

Advantage of using FSM

Using a finite state machine (FSM) for managing state offers several advantages over ad-hoc approaches (like scattered conditionals, flags, or event-driven code) and even over some object-oriented state patterns. Here are the key benefits:

  1. Clarity and Explicitness
    • All possible states and transitions are explicitly defined.
    • The system’s behavior is easy to visualize, reason about, and document.
    • Reduces ambiguity and hidden state changes.
  2. Predictability and Robustness
    • Transitions are controlled and validated.
    • Only allowed transitions can occur, preventing invalid or unexpected state changes.
    • Makes it easier to handle edge cases and errors.
  3. Maintainability
    • Adding or modifying states and transitions is straightforward.
    • Changes are localized to the FSM definition, not scattered across the codebase.
    • Reduces the risk of introducing bugs when requirements change.
  4. Testability
    • FSMs are easy to test.
    • You can systematically test all states and transitions.
    • Makes it easier to write unit tests for state-dependent logic.
  5. Separation of Concerns
    • State logic is separated from business logic.
    • Conditions and side effects are encapsulated, making the codebase cleaner and more modular.
  6. Scalability
    • FSMs scale well as complexity grows.
    • Adding new states or transitions does not exponentially increase code complexity, unlike nested if/else or switch statements.
  7. Visualization and Documentation
    • FSMs can be visualized as state diagrams.
    • This aids in communication with stakeholders and helps onboard new developers.
Approach Pros of FSM over this approach
If/else, switch Avoids spaghetti code, centralizes state logic
Flags/booleans Prevents invalid state combinations
Event-driven Makes allowed transitions explicit and predictable
State pattern FSM is more declarative and easier to visualize

Use Cases

Here are some common use cases for implementing a finite state machine (FSM) in software development:

  1. Workflow and Process Management
    • Example: Ticketing systems, order processing, approval workflows.
    • Why: Each item moves through a series of well-defined states (e.g., Open → In Progress → Resolved).
  2. User Interface (UI) Navigation
    • Example: Wizard dialogs, multi-step forms, menu navigation.
    • Why: UI components often have distinct states and transitions based on user actions.
  3. Game Development
    • Example: Character states (Idle, Walking, Jumping, Attacking), enemy AI behaviors.
    • Why: Game entities often have clear, rule-based state transitions.
  4. Protocol and Communication Handling
    • Example: Network protocol implementations (TCP handshake, HTTP request/response), parsers.
    • Why: Protocols are defined by sequences of states and transitions based on received data.
  5. Device and Hardware Control
    • Example: Embedded systems, robotics, IoT devices (e.g., a washing machine: Idle → Washing → Rinsing → Spinning → Done).
    • Why: Devices operate in modes with strict rules for moving between them.
  6. Authentication and Authorization Flows
    • Example: Login processes, multi-factor authentication, session management.
    • Why: Security flows require strict control over allowed transitions.
  7. Error Handling and Recovery
    • Example: Retry logic, circuit breakers, transaction management.
    • Why: Systems need to move between normal, error, and recovery states in a controlled way.
  8. Text Parsing and Lexical Analysis
    • Example: Tokenizers, interpreters, compilers.
    • Why: Parsing often involves moving through states based on input characters or tokens.

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