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AFSM

Inheritance

AFSM supports inheritance. Subclasses auto-merge the parent’s state diagram.

Basic inheritance

class Base extends FSM {
  @ChangeState(FSM.INIT, 'connected')
  async connect() {}


  @ChangeState([], 'disconnected')
  async disconnect() {}
}


class Advanced extends Base {
  @ChangeState('connected', 'authenticated')
  async authenticate() {}
}

Advanced’s stateDiagram includes all of Base’s edges plus its own authenticate edge.

stateDiagram merging logic

The stateDiagram getter, on first access:

  1. Reads the decorator metadata for the current prototype (from the stateDiagram Map)
  2. Recursively reads the parent prototype’s stateDiagram (via parent.stateDiagram)
  3. Merges all edges and states
  4. Caches via Object.defineProperties on the current prototype
// simplified pseudo-code
const proto = Object.getPrototypeOf(this)
const parentProto = Object.getPrototypeOf(proto)
if (stateDiagram.has(parentProto)) {
  parent.stateDiagram.forEach(line => result.add(line))
  parent.allStates.forEach(s => allState.add(s))
}
stateConfig.forEach(({ from, to, action }) => {
  // add current class's edges
})

allStates

allStates (also cached via Object.defineProperties) includes all known states:

  • All from and to states
  • All action + 'ing' intermediate states

Used by from: [] to generate “from every state into the intermediate” edges.

Caveats

Decorator metadata is per-prototype

const a = new Base()
const b = new Advanced()
a.stateDiagram   // only Base's edges
b.stateDiagram   // Base + Advanced edges

Cache is immutable

Object.defineProperties defines stateDiagram and allStates as value properties (non-writable, non-configurable). After first access, adding new @ChangeState won’t update the cache.

Subclasses can’t override parent transitions

If a subclass defines a same-named method, TS decorators register new metadata on the subclass prototype, but the parent’s metadata stays on the parent prototype. The stateDiagram getter reads both, potentially producing duplicate edges (deduped by Set).

Next steps