class FSM::ObserverRegistrar

• FSM::ObserverRegistrar
• Reference
• Object

Overview

Collects a Service's observers during construction, then goes inert.

Service.interpret yields one registrar to its builder block. The block registers observers into it, interpret copies them once into the Service, and interpret seals the registrar. This is the build-then-seal idiom the Machine and State builders use: a partially-built thing is registered inside the block and frozen at the end, so no caller can mutate observers on the live interpreter.

Both observers hold a single slot: the latest registration within the block replaces the previous one, the same last-write-wins semantics StateDefinition uses for on_entry and on_exit. The captured blocks are typed State ->; State is the runtime snapshot, which carries no generic parameter, so the registrar is not generic over T.

Once interpret has copied the observers and returned, the registrar is sealed and its registration methods raise SealedStateError, mirroring StateDefinition and Transition, whose builder methods raise once the machine seals them. An escaped registrar reference cannot mutate the live service's observers.

Sealing happens only on the successful path. If the setup block raises, interpret never reaches seal, and the registrar is discarded unsealed with no live object escaping the failed call. This matches Machine.build, which also abandons a half-built definition when its block raises rather than returning it.

Sealing guards post-construction misuse, not intra-block leaks. The registrar holds no internal lock, so a block that leaks the registrar to another fiber during construction is outside the guarantee, consistent with the project's stance that concurrency safety comes from sealing and single-owner access after construction, not from guarding intra-build escapes.

Defined in:

fsm/observer_registrar.cr

Instance Method Summary

• #on_event_processed(&block : State -> ) : self

  Register the observer fired after every step, regardless of outcome.

• #on_transition(&block : State -> ) : self

  Register the observer fired only when a transition actually occurred.

Instance Method Detail