Events

Platform spec node

Events

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Spec standingStandard

Owner

Piotr Mikstacki pmikstacki@cybernomad.it

Submitter

Piotr Mikstacki pmikstacki@cybernomad.it

Current document

ADRs

No architecture decision records under adr/ for this feature yet. Standard features must publish at least one ADR or keep a ## Decisions summary on the hub.

Articles

• Control flow Conditionals, loops, and structured control transfer. Lowering to HIR/CLIF follows the evaluation order defined here. article Standard Reviewed Thu May 21
• Events Multicast events, subscription lifetime, and thread affinity assumptions. UI stacks build on these primitives. article Standard Reviewed Thu May 21
• Lambdas and closures Capture lists, environment layout, and lifetime of delegates. JIT and AOT must agree on closure calling conventions. article Standard Reviewed Thu May 21

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Completeness

OKarea · 2 SpecSection(s) · 0 H2 heading(s)

Section id	Required	Found
scope	yes	yes
features	yes	yes

Full tree: run pnpm verify:platform-spec-layout (writes src/generated/platform-spec-layout-report.json).

Related spec docs

• Area
  Evaluation

  Parent area

• Domain
  Language meta

  Parent domain hub

• Domain
  Platform specification

  Cross-cutting index

• Domain
  Execution documentation

  Non-normative legacy execution bridge

Normative specification

Scope

Defines event fields on types and their raise/subscribe surface. Fiber cancellation events are specified in Fibers and spawn and the concurrency package.

Declaration

• event Name(params); on a type declares a multicast callback slot.
• Optional event {N} Name sets a capacity hint (EventCapacity); runtime may use this for bounded subscriber lists.
• Event fields are not ordinary value fields; they must not be read like variables.

Static rules

• Raising or subscribing must target an in-scope event member on a value or this-equivalent receiver.
• Event signatures must use parameter lists compatible with delegate lowering (no ref/out on event parameters unless explicitly allowed by host profile).

Dynamic semantics

• Multicast: Multiple subscribers may be registered; raise must invoke subscribers in registration order unless a host profile defines fairness.
• Synchrony: Unless a host documents otherwise, event handlers run on the raising fiber and must not block on Join of self.
• Lifetime: Subscriptions should be detached when the owning object is disposed; leaks are host-defined (corelib hosts document behavior).

Diagnostics

Event misuse must surface as member/type errors (E1213 family) until a dedicated event band is allocated.

Conformance

Types with event fields must lower to the same calling convention in AOT and JIT for a given target.

Decisions

• D-LM-EVT-001 — Language event keyword: Events are fields, not separate delegate types in user syntax.
• D-LM-EVT-002 — Fiber OnCancelled: Cancellation uses the same event mechanism on Fiber<T> per concurrency decisions record.
• D-LM-EVT-003 — Synchronous default: Handlers run on the raising fiber unless a host profile says otherwise.
• D-LM-EVT-004 — Not Option: Subscription state is host-managed; absence of subscribers is not Option<T> at the language surface.

Platform view

Multicast events, subscription lifetime, and thread affinity assumptions. UI stacks build on these primitives.