Enum UserdataPayload 

pub enum UserdataPayload {
    File(FileHandle),
    Empty,
    Host {
        type_id: TypeId,
        data: Box<dyn Any + 'static>,
        trace_fn: Option<fn(&(dyn Any + 'static), &mut UserdataMarker<'_>)>,
    },
}

A userdata’s host-side payload. Beyond io file handles luna exposes:

• Empty — PUC 5.1 newproxy() carries only identity + an optional metatable hook for __index / __newindex / __gc.
• Host — embedder-supplied Rust value (v1.1 B8). The host owns the value; luna treats it as opaque Any. v1.1 restricts host types to 'static non-GC-bearing types; Trace-bearing host payloads land in Phase 4+ alongside the userdata GC ripple.

Variants

File(FileHandle)

an io stream/file handle

Empty

a PUC 5.1 newproxy userdata — no host payload, only identity

Host

B8 — embedder-supplied Rust value. type_id keys the downcast; data is the boxed payload.

Fields

type_id: TypeId

TypeId of the host value, used as the downcast key.

data: Box<dyn Any + 'static>

Boxed host payload (the embedder owns the underlying data semantically; luna treats it as opaque Any).

trace_fn: Option<fn(&(dyn Any + 'static), &mut UserdataMarker<'_>)>

Trace adapter for the concrete T keyed by type_id. Captured by crate::vm::Vm::create_userdata as a monomorphic fn(&dyn Any, &mut UserdataMarker) whose body downcasts the payload to &T and calls crate::vm::LuaUserdata::trace.

None means “no trace adapter wired” — only possible for payloads constructed via the v1.1 crate::runtime::heap::Heap::new_userdata path that bypasses the trait sugar (none exist in luna today, but the Option preserves source-compat for any external crate that built a UserdataPayload::Host literal under the v1.2 shape).

Phase TB (v1.3) — see .dev/rfcs/v1.3-audit-trace-bearing-userdata.md.