💡 LogicBlocks

LogicBlocks is a serializable, hierarchical state machine package for C# that works well when targeting ahead-of-time (AOT) environments. LogicBlocks draws inspiration from statecharts, state machines, and blocs.

Instead of elaborate transition tables, states are simply defined as self-contained class records that read like ordinary code using the state pattern. Logic blocks are designed with performance, adaptability, and error tolerance in mind, making them refactor-friendly and suitable for high performance scenarios (such as games).

Logic blocks grow with your code: you can start with a simple state machine and easily scale it into a nested, hierarchical statechart that represents a more complex system — even while you're working out what the system should be.

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📚 What to Read Next

Logic blocks are based on statecharts. You may also know them as hierarchical state machines (HSM's).

• 🟢 Introduction to State Machines and Statecharts

  Beginner: overview for those who are new to statecharts.

• 🟡 Statecharts.dev

  Intermediate: all the statechart concepts in one place.

• 🔴 UML State Machine (Wikipedia)

  Expert: all the juicy technical details are here.

• 🔵 Logic Blocks Timer Tutorial

  In a hurry? Learn about hierarchical states and logic blocks all at once!

💡 Example

A logic block is a class that receives inputs, maintains a single state instance, and produces outputs.

Logic blocks enable you to efficiently model complex behaviors¹.

using Chickensoft.Introspection;

[Meta, LogicBlock(typeof(State), Diagram = true)]
public class LightSwitch : LogicBlock<LightSwitch.State> {
  public override Transition GetInitialState() => To<State.PoweredOff>();

  public static class Input {
    public readonly record struct Toggle;
  }

  public abstract record State : StateLogic<State> {
    public record PoweredOn : State, IGet<Input.Toggle> {
      public Transition On(in Input.Toggle input) => To<PoweredOff>();
    }

    public record PoweredOff : State, IGet<Input.Toggle> {
      public Transition On(in Input.Toggle input) => To<PoweredOn>();
    }
  }

  public static class Output {
    public readonly record struct StatusChanged(bool IsOn);
  }
}

🖼️ Visualizing Logic Blocks

LogicBlocks provides a source generator that can generate UML state diagrams of your code.

Generated UML diagrams are placed alongside the code for your logic block with the *.g.puml extension. You can use PlantUML (and/or the PlantUML VSCode Extension) to visualize the generated diagram code.

tip

A diagram explains all of the high level behavior of a state machine in a single picture. Without a diagram, you would have to read and scroll through all the relevant code files to understand the machine (especially if you weren't the author, or forgot how it worked since you had written it).

🤫 Differences from Statecharts

In the interest of convenience, logic blocks have a few subtle differences from statecharts:

• 💂‍♀️ No explicit guards

  Use conditional logic in an input handler

• 🪢 Attach/Detach callbacks

  These are an implementation specific detail that are called whenever the state instance changes, as opposed to only being called when the state type hierarchy (i.e., state configuration) changes.

• 🕰️ No event deferral

  Non-handled inputs are simply discarded. There's nothing to stop you from implementing input buffering on your own, though: you may even use the boxless queue collection that LogicBlocks uses internally.

LogicBlocks also uses different terms for some of the statechart concepts to make them more intuitive or disambiguate them from other C# terminology.

statecharts	logic blocks
internal transition	self transition
event	input
action	output

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1. Simple behaviors, like the light switch example, are considerably more verbose than they need to be. Logic blocks shine brightest when they're used for things that actually require hierarchical state machines.↩